In a post on his Truth Social platform, the US president warned against the loss of the US-UK military base on Diego Garcia, which the UK is retaining through a 99-year lease of the island.
"Our relationship with the United Kingdom is a strong and powerful one, and it has been for many years, but prime minister Starmer is losing control of this important Island by claims of entities never known of before," said Mr Trump.
Mr Trump said that Sir Keir "should not lose control, for any reason, of Diego Garcia, by entering a tenuous, at best, 100 Year Lease".
He added: "This land should not be taken away from the U.K. and, if it is allowed to be, it will be a blight on our Great Ally. We will always be ready, willing, and able to fight for the U.K., but they have to remain strong in the face of Wokeism, and other problems put before them.
"DO NOT GIVE AWAY DIEGO GARCIA!"
The UK government has defended the deal following Mr Trump's post.
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What is in the Chagos Islands deal criticised by Donald Trump - and why is it controversial?
A Foreign, Commonwealth and Development Office spokesperson said: "The deal to secure the joint UK-US military base on Diego Garcia military is crucial to the security of the UK and our key allies, and to keeping the British people safe.
"The agreement we have reached is the only way to guarantee the long-term future of this vital military base."
Sky's US correspondent Mark Stone says the post will be a "difficult read" for the UK government, who are "exasperated by the flip-flopping that has gone on".
The Chagos Islands are an archipelago in the Indian Ocean, with the island of Diego Garcia home to a joint UK-US military base.
The islands are an overseas territory of the UK, but after the UK lost a court case over the sovereignty of the islands, the government agreed to cede the islands to Mauritius.
Changing US position on Chagos Islands deal
The US backed the deal to give sovereignty of the islands to Mauritius as recently as Tuesday.
A spokesperson for the US State Department said then: "The United States supports the decision of the United Kingdom to proceed with its agreement with Mauritius concerning the Chagos archipelago."
Mr Trump previously criticised the deal in January, calling it an "act of total weakness" and "great stupidity" - although following a phone call with Sir Keir on 5 February, he signalled his support for the deal, calling it "the best [Sir Keir] could make".
Asked by reporters whether Mr Trump's post meant the US position on the Chagos Islands deal had changed, White House press secretary Karoline Leavitt said: "The post should be taken as the policy of the Trump administration, it's coming straight from the horse's mouth."
Sky News understands that Conservative MP Sir Iain Duncan Smith, who is a strong opponent of the deal, has just returned from Washington DC where he lobbied the White House, National Security Council, and State Department on the issue.
'Kill this terrible deal,' says Badenoch
The law to formally give away the islands is still before parliament, and the issue has become a significant political row.
The Conservatives and Reform UK both oppose the deal, while the Liberal Democrats have demanded MPs are given a fresh vote on the issue.
Responding to Mr Trump's latest comments, Tory leader Kemi Badenoch said the US president was "right".
"Chagos is a strategic asset. If our closest ally is saying this, the PM should listen. It's time to kill this terrible deal," she added.
But Liberal Democrat leader Sir Ed Davey criticised Mr Trump's changing position: "Trump's endless flip-flopping on the Chagos Islands shows why Starmer's approach is doomed to fail. Britain can't rely on the US while Trump is in the White House."
Reform UK leader Nigel Farage said: "Keir Starmer risks alienating our most important ally by giving away the Chagos Islands, the worst deal in British history... Starmer must cancel this deal."
The House of Lords inflicted four defeats on the government last month on the details of the leasing of Diego Garcia - and the publication of any detailed payments made to Mauritius.
The government pulled the bill from the Lords, and has yet to reschedule it.
But at that time, there was almost no US military presence that would have made a difference in the region.
On 22 January, he said there was a "great armada" assembling, when what he was referring to was the aircraft carrier, the USS Abraham Lincoln and its attendant Carrier Strike Group 3.
None of it matched his rhetoric. But by this weekend, it will have done so, as a powerful US military force assembles within striking distance of Iran. It has three main elements.
First is the naval force. The Lincoln and its CSG 3 will shortly be joined by the USS Gerald Ford, and its attendant CSG 12. The USS Ford is passing through the Gibraltar Strait in the next 24 hours and can be expected to be on station south of Cyprus in about four days, travelling at normal cruising speed.
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These two Nimitz-class carriers (CVN 72 and CVN 78) will be bringing extra air defence and Tomahawk-carrying destroyers with them, bringing the number of known, and named, US destroyers in the region to 11. They will join three Littoral Combat Ships already on station and a good number of support ships as well. In addition, each CSG includes - though never usually named - a nuclear attack submarine (an SSN), probably of the Virginia class.
And there may also be an Ohio-class SSN in the area, which is specifically designed to launch Tomahawk and other missiles at land targets.
The second element has been provided over the previous 10 days by an extensive series of C-5 and C-17, Galaxy and Globemaster flights in and out of the region, bringing air defence assets to US bases, presumably as cover in the event of any Iranian retaliation in response to potential US attacks. Israeli "Iron Dome" air defence batteries have also been moved from its frontier with Gaza to its borders in the east, probably for the same reason.
And thirdly, the US has sent an extensive force of KC-130 air-to-air refuelling tankers to bolster its existing air tanker force. They left from the British base at Mildenhall (six tankers on 16 February) to Greece, and (on 18 February) no fewer than 10 more came from bases in the continental United States, via Britain, to bases in Greece and Bulgaria. In addition, US aircraft are known to be in the British base at Akrotiri in Cyprus, at Aviano in Italy, in the Azores, in Spain and at the Chagos Island base of Diego Garcia. Well over 100 US combat aircraft - F-15s, F18s, F-22s, F35s and B2 bombers - are now available to US military planners in the potential theatre of operations.
But the extra KC-130 tankers are the giveaway. They give away the possibility that US aircraft might be operating from bases not sited on the territories of America's Middle East allies, but from less politically sensitive bases further away. And they give away the possibility that any air campaign might be quite prolonged, not just a sudden one-off attack.
The final piece of the jigsaw: no fewer than six E3 Sentry aircraft. These flying control centres can survey and control everything that happens beneath them. They are, in effect, flying HQ's and a country can run a war from one of them. By the weekend, there will be a lot for these six E3 Sentry aircraft to look at and control.
What all this military power will be used for is still a matter of some speculation.
What does the tracking data show us?
By Freya Gibson, junior OSINT producer
Sky News Data & Forensics team has tracked the locations of US military planes and ships heading to the region in recent days and weeks.
Several US Navy boats have been sent to the Middle East, including the USS Abraham Lincoln, a nuclear-powered aircraft carrier that carries 90 aircraft, including F35 fighters, and 5,680 crew. The Lincoln is leading a carrier strike group which includes three destroyers. The ship was last seen in the Arabian Sea around 240km off the coast of Oman. Sky News confirmed the location of this ship on 15 January.
In addition, the USS Gerald R Ford, the lead ship of the US Navy's nuclear-powered aircraft carriers, is en route to the Middle East. Sky News has confirmed its latest location as tracking shows the Ford was around 600km from the Strait of Gibraltar at 1.58pm on 18 January. This aircraft carrier, like the USS Abraham Lincoln, also forms a carrier strike group that includes three destroyers. In total, there are reported to be more than 12 US ships now in the Middle East.
Sky News has also tracked movements of US aircraft in the region. More than 15 refuelling tankers have repositioned towards the Middle East and Europe since 16 January. These aircraft, the K-135s, are aerial refuelling aircraft. They can carry up to 200,000 pounds of fuel and 83,000 pounds of cargo. They have four engines and operate at speeds up to 530mph and altitudes up to 50,000 feet.
The aircraft came from multiple locations, including RAF Mildenhall in the UK, Tampa in Florida and Sioux City in Iowa. They have been landing in different locations, including Chania Airport in Greece and Sofia Airport in Bulgaria.
Satellite imagery shows F-15s and A-10 Thunderbolts at Muwaffaq Salti Air Base, Jordan. They can conduct precision airstrikes and engage armoured targets, alongside C-130 transport aircraft providing logistical support.
What is Iran doing?
Sky News has tracked the positions of Iranian Navy vessels using data from TankerTrackers. Around six vessels can be seen just off the coast of Bandar Abbas on 16 January. One of these ships is an Iranian Drone Carrier, IRIS Shahid Bagheri. Satellite imagery confirmed its location on 16 January, 10km from the coast.
It is often spotted around this location in the Strait of Hormuz. It can deploy roughly 60 drones along with helicopters.
The 25-year-old left the field during Real Madrid's Champions League play-off in Lisbon on Tuesday after reporting Benfica winger Gianluca Prestianni to the referee.
But Benfica manager Mourinho appeared apportion some blame to Vinicius, telling reporters afterwards: "A stadium where Vinicius plays, something happens, always."
On Wednesday, former France international Silvestre told Sky News that Mourinho was trying to mislead fans with his comments.
“In terms of what high level and reputation he has, Jose Mourinho failed us," Silvestre told chief presenter Mark Austin. "As an industry, and as human beings, he completely misled everyone - or he tried.
“But we are not foolish - and we know what happened."
Prestianni, however, has denied making racist comments towards Vinicius, claiming he was "misunderstood" by his opponent.
Mourinho also came under fire for claiming Vinicius had provoked the abuse with his celebration after scoring the only goal early in the second half.
The Brazilian danced around the corner flag, an apparent nod to Cameroonian Roger Milla's iconic World Cup celebration.
Mourinho told Amazon Prime: "I told him, when you score a goal like that, you just celebrate and walk back."
Silvestre hit back against the former Manchester United manager, adding: "For Jose Mourinho to divert and even vilify Vinicius Junior behaviour for celebrating the goal that he did - remembering Roger Milla for Cameroon years ago - it's not the way a top manager like him should do.
"We expect better, clearly it was bad for everyone, and I hope he's regretting his comment during the game, and also after during the press conference."
Silvestre is a member on the FIFA Player’s Voice Panel, tasked with advising on on-pitch racism incidents, alongside legends such as George Weah and Didier Drogba.
Prestianni's response to abuse allegation
In a statement in Portuguese on Instagram, shared by Benfica on social media, Prestianni denied he made any racist comments.
He wrote: “I want to clarify that at no time did I direct racist insults to Vinicius Junior, who regrettably misunderstood what he thought he heard.
“I was never racist with anyone and I regret the threats I received from Real Madrid players.”
Prime Minister Sir Keir Starmer said he was putting tech companies "on notice" to take down non-consensual intimate images, and will leave "no stone unturned" to protect women and girls.
Companies will be legally required by law to remove the images within 48 hours of them being reported to them.
If they do not, firms could be fined 10% of qualifying worldwide revenue - which could amount to billions of pounds for some major platforms - or have their services banned from the UK.
Ministers say tech firms should take tackling intimate image abuse as seriously as they take tackling terrorist or child sexual abuse material.
The government is making the change through an amendment to the Crime and Policing Bill, which is currently going through parliament.
Media regulator Ofcom is also considering plans to treat non-consensual intimate images as the same as child sexual abuse material, which is digitally marked when found, so that any time they are re-shared, they are automatically taken down.
Additionally, the government says it will publish guidance for internet companies on how to block "rogue websites" that host this content and fall out of reach of the Online Safety Act.
Sir Keir said he would "leave no stone unturned in the fight to protect women from violence and abuse".
He said the government had already taken "urgent action against chatbots and 'nudification' tools", and that they were "going further, putting companies on notice so that any non-consensual image is taken down in under 48 hours".
Technology Secretary Liz Kendall said: "The days of tech firms having a free pass are over... No woman should have to chase platform after platform, waiting days for an image to come down."
Shadow technology secretary Julia Lopez said when a similar proposal was put forward by Conservative peer, Baroness Charlotte Owen, Labour had failed to take action.
"Once again, the government is playing catch-up to duck a major backbench rebellion.
"The reality is that, for all the prime minister's tough rhetoric, he has arrived late to this issue. He does not know what to believe - he only knows what to do to try and survive another week."
The move follows controversy in January over X's AI tool, Grok, creating AI images undressing people without their consent.
Creating non-consensual intimate images, including sexually explicit deepfakes, was criminalised earlier this month, and X stopped Grok from creating the images following the outrage.
Other countries are also taking action against X, with Ireland's data privacy regulator saying on Tuesday that X faces an EU privacy investigation over the non-consensual deepfakes created by Grok.
Earlier this week, Sir Keir announced a crackdown on social media platforms, such as closing a legal loophole to eliminate "vile illegal content created by AI".
Downing Street has also launched a consultation on measures like an Australian-style ban on under-16s using social media, and is ensuring it is able to implement one quickly if it is recommended.
The avalanche hit the Castle Peak area of Truckee in California, about 10 miles (16km) north of Lake Tahoe, at around 11.30am local time on Tuesday.
The cascade engulfed a group of off-piste skiers, with six people being rescued after they became trapped.
Authorities were still searching for nine missing people on Wednesday morning local time, but have since confirmed eight fatalities and one unaccounted for.
"Eight of the additional nine skiers have been located deceased," Nevada County sheriff Shannan Moon said. "We are still looking for one of the members at this time."
Ms Moon said the "horrific conditions", and the risk of further avalanches, had hampered rescue efforts.
The eight dead skiers were found with their beacons active, and their bodies will be recovered when conditions improve.
One was married to a member of the search-and-rescue team, authorities said.
The group of 15 skiers - who were outside ski resort boundaries - were returning from a three-day excursion when the avalanche struck, the organising tour company Blackbird Mountain Guides said.
The rescued skiers - including one guide and five clients - had taken refuge in a makeshift shelter made from tarpaulin sheets and communicated with authorities using a radio beacon and text messaging.
The survivors located three others who had died, Ms Moon said.
Two of them were unable to walk because of their injuries, and were taken to hospital, she added.
One person had been stabilised and released on Tuesday night, while another person remained in hospital.
The survivors include five women and one man, authorities said.
Rescuers used a snowcat to get within two miles (3.2km) of the survivors, and skied the remaining distance to avoid causing another avalanche.
Ms Moon said the investigators would look into the decision to proceed with the trip despite the weather forecast.
"We're still in conversation with them on the decision factors that they made," she said.
She said it was initially believed that 16 people had been on the tour, but the number was revised to 15 after it was confirmed that one person had pulled out at the last minute.
Avalanche warning issued
California has been hit by a powerful storm this week, bringing heavy snow, high winds and severe thunderstorms to the mountainous region.
The Sierra Avalanche Center issued an avalanche warning for the area in the Central Sierra Nevada, starting on Tuesday at 5am local time, with large slides expected into Wednesday.
The rapid accumulation of snow in unstable layers, coupled with gale-force winds, had produced the dangerous conditions.
The area near Donner Summit has one of the highest snowfalls in the Western Hemisphere, with an average of nearly 35ft (10m) of snow a year.
The area is named after the infamous Donner Party, a group of pioneers who resorted to cannibalism after becoming trapped in the winter of 1846 to 1847.
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The incident marks the deadliest avalanche in the US since 1981, when 11 climbers were killed on Mount Rainier in Washington.
Each winter, between 25 to 30 people die in avalanches in the US, according to the National Avalanche Center.