The US president said 10% tariffs would come into effect on 1 February for Denmark, Norway, Sweden, France, Germany, the UK, the Netherlands and Finland.
The rate would then climb to 25% on 1 June if no deal was in place for "the complete and total purchase of Greenland" by the United States, Mr Trump wrote in a lengthy post on his Truth Social platform on Saturday.
Trump threatens tariffs over Greenland - as it happened
The US president seems to have acted on his previous warning that he would impose tariffs on countries that do not go along with his plan to acquire the Danish territory.
Prime Minister Sir Keir Starmer said Mr Trump was "completely wrong" for applying tariffs on allies who are "pursuing the collective security of NATO allies", adding that he will be "pursuing" this with the US administration.
French President Emmanuel Macron called the threat of tariffs "unacceptable" and said if implemented Europe would respond in a coordinated manner.
European Commission president Ursula von der Leyen and European Council president Antonio Costa said in separate but identical posts on X that the European Union stood in "full solidarity" with Denmark and Greenland.
"Tariffs would undermine transatlantic relations and risk a dangerous downward spiral. Europe will remain united, coordinated, and committed to upholding its sovereignty," they said.
Officials from Norway, Sweden, France and Germany reiterated support for Denmark and said tariffs should not be part of Greenland discussions.
Tory leader Kemi Badenoch said Mr Trump was "completely wrong" to impose tariffs, adding they would be a "burden for businesses across our country".
Reform leader Nigel Farage said the tariffs would "hurt" the UK, and Liberal Democrat leader Sir Ed Davey said Mr Trump was "punishing" the UK.
The European Union has called an emergency meeting of ambassadors from the 27-member countries for Sunday following Mr Trump's announcement.
The US president indicated the tariffs were a retaliation after European countries sent military personnel to Greenland in a show of support for the territory.
He wrote: "These countries, who are playing this very dangerous game, have put a level of risk in play that is not tenable or sustainable."
So far France has sent as many as 15 personnel to the Danish territory, Germany has sent 13 and the UK has sent one military officer.
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'Hands off' Greenland protests
The tariffs were announced the same day thousands of people marched through Copenhagen in support of Greenland in the face of threats from Mr Trump.
Demonstrators brandished Danish and Greenlandic flags and signs with slogans including "Make America Smart Again" and "Hands off" as they marched on Saturday afternoon.
Other rallies were planned in Nuuk, the Greenlandic capital, and elsewhere in the Danish kingdom.
"This is important for the whole world," Danish protester Elise Riechie said, as she held Danish and Greenlandic flags.
"There are many small countries. None of them are for sale."
The protests come as a bipartisan US congressional delegation sought to reassure Denmark and Greenland of their support.
Delegation leader senator Chris Coons, a Delaware Democrat, said he wanted to de-escalate the situation and the US had respect for Denmark and NATO "for all we've done together".
"I hope that the people of the Kingdom of Denmark do not abandon their faith in the American people," Mr Coons said in Copenhagen.
Mr Trump has repeatedly argued the US needs to take over Greenland because Russia and China had their own designs on the self-governing territory.
The president's comments stood in stark contrast to Mr Coons's remarks on Saturday.
Read more:
Why does Trump want to take over Greenland?
Trump is likely gambling he could get away with Greenland grab
"There are no current security threats to Greenland," Mr Coons said.
The White House has not ruled out taking Greenland - which has vast untapped reserves of critical minerals - by force.
"There is almost no better ally to the United States than Denmark," Mr Coons said. "If we do things that cause Danes to question whether we can be counted on as a NATO ally, why would any other country seek to be our ally or believe in our representations?"
Earlier this week, the foreign ministers of Denmark and Greenland met with US vice president JD Vance and secretary of state Marco Rubio in Washington.
That meeting resulted in an agreement to set up a working group, despite Denmark and the White House offering diverging views on its purpose.
Denmark said this week it was increasing its military presence in Greenland in co-operation with allies.
Donald Trump, he has said, is "completely wrong" to slap tariffs on the UK and other European countries "for pursuing the collective security of NATO allies."
He's not going as far as President Macron, who has pledged never to change course in the face of "intimidation or threat".
But while the PM has previously been clear about the UK's staunch support for Denmark - he's always usually very cautious in his dealings with the mercurial president.
Starmer has invested huge political capital and personal energy in developing a personal connection with Donald Trump, despite their obvious differences.
Indeed the PM's efforts at strengthening the so-called special relationship - particularly in the service of Ukraine - have been widely seen as one of the more successful aspects of his bumpy premiership thus far.
But that relationship has become decidedly abusive - Trump accuses the UK and other European allies of "playing a very dangerous game" in travelling to Greenland "for purposes unknown".
The UK has sent just one single military officer to Greenland to carry out a reconnaissance mission ahead of a future joint exercise in the area, alongside a handful of troops from other countries.
While this was clearly done in solidarity with the Danes and Greenlanders, the idea was also precisely to demonstrate that NATO has been listening to the president's concerns about Greenland. The PM's statement stressed he has "made [it] clear that Arctic Security matters for the whole of NATO and allies should all do more together to address the threat from Russia".
It's a topic he has repeatedly discussed in phone calls with Trump and other European leaders over the past few weeks, following the White House's resurgent interest in Greenland.
But it's clear from the president's Truth Social post that no amount of NATO positioning - certainly not a handful of soldiers on a training exercise - is going to change his mind. He's now absolutely fixated on taking over Greenland - commandeering what would be the 51st state of the US.
In such extraordinary circumstances, Sir Keir Starmer's key political opponents have actually come out in support of his position on Greenland - and against Trump.
Conservative leader Kemi Badenoch said she agreed with him, also describing Trump's approach as "completely wrong". Nigel Farage said Reform UK "certainly don't" agree with the US government.
Liberal Democrat Ed Davey, who has a long track record in criticising the government's cosy relationship with Donald Trump, called for "the PM to stand firm against the bully in the White House".
Read more:
Why does Trump want to take over Greenland?
Poll reveals what Americans think about Greenland scheme
Trump says US will act on Greenland 'whether they like it or not'
Many backbenchers have been much more gung-ho in their insults and calls for action. Former Lib Dem leader Tim Farron asked "if Starmer, Badenoch and Farage *still* think it's worth shamelessly appeasing this wombat?"
Conservative backbencher Simon Hoare described Trump as a "gangster pirate" and called for the King's visit to be cancelled.
Tory former army officer Ben Obese-Jecty MP demanded the PM "defend British interests" and questioned why the Americans had reduced the number of their troops based in Greenland from thousands to around 150 if its security is really so important to the US.
In perhaps the most scathing assessment, Conservative MP Alicia Kearns MP asked "what has all Labour's sycophantic fawning achieved in the national interest?"
That's surely a raw question in Downing Street this weekend as the PM and his team attempt to strategise their response. How can they really stand up to an American president on the march under the threat of an international trade war? Further tariffs of 10 and 25% - presumably on top of the existing 10% tariff on most baseline goods exported to the US - will hardly help in the mission to drive growth into the tottering British economy.
Could we see an emergency visit to Washington by the group of leaders, as they did last summer in support of President Zelenskyy? Might Italian Prime Minister Georgia Meloni, not currently on Donald Trump's hit list, be prevailed upon to use her own influence with the US? Is there any more ring-kissing that can be done? Counter tariffs? Or will they be forced to capitulate - and give up Greenland, and the principle of NATO solidarity with it?
Whatever happens, Donald Trump has made his position abundantly clear. The path for European leaders is much less so.
Meraj Tehrani, who lives in the UK, told Sky News' international correspondent Alex Rossi he returned to Iran on business in early January, as demonstrations were erupting across the country.
Initially motivated by the country's ailing economy, the demonstrations have grown to challenge the ruling regime itself, leading to violence in the streets.
Iran latest: Khamenei admits thousands died in protests
On Saturday, Iran's Supreme Leader Ali Khameni acknowledged "several thousand people" had been killed in the protests.
In their latest figures, the US-based Human Rights Activists News Agency group said it had verified 3,090 deaths, including 2,885 protesters, from the demonstrations and subsequent crackdown.
Tehrani told Sky News: "At first I think the government didn't believe that so many people would come out, they were surprised."
He said the internet shut down quickly after "millions" of people turned out.
The musician said people from all walks of life are calling for change, describing the country as undergoing a complete transformation.
"I've never seen an Iranian mood like that," he said. "Everyone was united, everyone was hoping, 'This is the time'. Everyone was chanting together for the first time."
He said he saw non-lethal bullets and tear gas being used by authorities, but said the violence then escalated.
"On Friday evening [9 January], that's when the majority of the killing started," said Tehrani.
He said it was when the revolutionary guard came out, "that's when everything got serious", and it became "a massacre on the streets".
Describing a video he had seen of "bullets shooting and killing people", he said bodies were "left on the street for the others to look at, so they get panicked and scared and it is a lesson for them, 'You are next if you're coming out on the street'… If you come out and demonstrate again, you will be like this guy, this lady, this woman, this kid."
He also said "machine guns" were used to shoot protesters at random.
Tehrani said he believed foreign forces - including Iraqi militia, the Popular Mobilisation Forces in Iraq - have been brought in by the regime to stop the protests.
He said: "That is why they know how to fight, [shooting at] heads and chest, heads and chest."
He described the guards doing the killing as "different" to the normal guards.
He said: "One person's life matters in any nation, and thousands of people have been killed in a very aggressive way."
Describing the regime's days as numbered, maybe "less than two months", he said Iran felt let down by the international community, asking: "Where is the European Union? Where is Keir Starmer? I've never seen him put down any statement."
As for those who came out to protest after US President Donald Trump's statement of support on Tuesday, he said Iranians felt "a bit let down, but we have hope".
Tehrani said he received threatening messages on social media and said he would not be going back to Iran, adding: "If I go back, they will catch me and hang me."
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Despite that, he said he would be a voice for his people, saying: "The whole world needs to understand and hear us. How can we be terrorists? We just want a better life. We just want freedom."
In comments carried by Iranian state media, Iran's Ayatollah Ali Khamenei accused "those linked to Israel and US" for causing "massive damages" and killing "several thousands" during unrest.
Earlier on X, Khamenei said he held President Trump responsible for the "casualties, damages and slander he has levelled against the Iranian nation" during protests.
He said the recent unrest was caused by "American sedition", the goal of which "is to swallow Iran".
"The Iranian nation broke the back of sedition; it must also break the back of the seditionists," he said.
"We are not leading the country to war, but we will not abandon the domestic and international criminals of American sedition either."
Bilal Hasan al Jasim had direct links to the ambush, which killed two US soldiers and a civilian interpreter in Syria, according to officials.
Now he too has been killed in a third round of retaliatory strikes in Syria, which targeted the northwest of the country on Friday.
US Central Command (CENTCOM) described Jasim as "an experienced terrorist leader who plotted attacks and was directly connected" to the 13 December ambush.
"The death of a terrorist operative linked to the deaths of three Americans demonstrates our resolve in pursuing terrorists who attack our forces," said Admiral Brad Cooper, CENTCOM commander.
"There is no safe place for those who conduct, plot, or inspire attacks on American citizens and our warfighters. We will find you."
Defence secretary Pete Hegseth, in a post on X, added: "We will never forget, and never relent".
The ambush last month killed Sgt Edgar Brian Torres-Tovar, Sgt William Nathaniel Howard and civilian interpreter Ayad Mansoor Sakat.
In the aftermath, Donald Trump launched an operation against "ISIS thugs" who were regrouping after Syrian dictator Bashar al Assad was deposed in December 2024.
Read more:
US carries out large-scale strikes against IS targets in Syria
British forces bomb underground IS facility in Syria
The US president emphasised that American forces were fighting alongside Syrian troops, and that Syrian president Ahmed al Sharaa was "extremely angry" about the ambush.
So far, the US military claims to have hit more than 100 ISIS targets in Syria.
It comes as the Met Office said this weekend, temperatures will be mostly average, with showers on Saturday and temperatures ranging from 6C to 10C (42.8F to 50F).
Met Office meteorologist Honor Criswick said that Sunday would be a "very cloudy and grey day" with dense fog, and rain moving in as the day progressed.
"Spells of rain eventually pushing into southern England and Wales, pushing northwards through the day, this could turn a little bit heavy at times," she said.
Check out the weather forecast where you are
Though southeast England, northwest Scotland, and Northern Ireland would see some bright spells, temperatures would be lower overall, between 2C to 6C (35.6F to 42.8F).
But conditions could turn colder later in the month, increasing the "chance of snow across parts of the country".
The Met Office said that from Thursday 22 January, the UK will see a "battle between Atlantic weather systems attempting to arrive from the west while high pressure and colder conditions attempt to exert some influence from the east".
Initially, milder Atlantic air is expected to dominate, with cloudy, changeable conditions with showers and average temperatures, the weather agency said.
Then towards the end of the month, there is an increased chance that it will turn colder, with the potential for snow.
The Met Office said: "This aspect of the forecast is still somewhat uncertain but the potential transition to colder weather also increases the chance of snow across parts of the country."
People can also expect an increased chance of cold conditions in February and the "associated risk of wintry hazards at times".
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Earlier this month, the UK was battered by Storm Goretti, described as a "multi-hazard event" by the Met Office, which brought gusts of almost 100mph and a rare red warning for "dangerous, stormy" winds in the southwest of England.
A man in his 50s was found dead in a caravan after a tree fell on to the vehicle in Helston in Cornwall, police said.
The conditions caused flights to be cancelled, trains disrupted and hundreds of schools closed due to the wintry weather.