Trump said the UK and seven other European nations will be charged a 10 per cent tariff "on any and all goods" sent to the US from February 1, increased to 25 per cent from June 1, until a deal is reached for Washington to purchase Greenland from Denmark.
He said it would also apply to Denmark, Norway, Sweden, France, Germany, the Netherlands, and Finland, and that they had "journeyed to Greenland, for purposes unknown".
Starmer said in response Greenland was part of Denmark and its future was a matter for Greenlanders and Danes.
"We have also made clear that Arctic Security matters for the whole of NATO and allies should all do more together to address the threat from Russia across different parts of the Arctic," he said in a post on social media platform X.
"Applying tariffs on allies for pursuing the collective security of NATO allies is completely wrong. We will of course be pursuing this directly with the US administration."
French President Emmanuel Macron also responded sharply to Trump's tariff declaration.
"Tariff threats are unacceptable and have no place in this context," Macron wrote in a post on X, vowing "a united and co-ordinated" European response.
France is committed to the sovereignty and independence of nations in Europe and elsewhere and has therefore joined the military exercise initiated by Denmark in Greenland, Macron said.
"We stand by this. Also because it concerns security in the Arctic and at Europe's borders."
Swedish Prime Minister Ulf Kristersson said only Greenland and Denmark would decide on issues affecting them, and vowed to stand up for his country and its allied neighbours.
"We will not be blackmailed," Kristersson wrote on X.
Though Washington has been ratcheting up pressure over its plans for Greenland, US reports suggest the countries were given no notice of what was coming.
Kristersson said his country was having "intensive discussions" with the other nations to decide on a co-ordinated response, while French President Emmanuel Macron said he would hold talks with European partners.
Earlier this week, the UK confirmed it had sent a military officer to Greenland as Denmark stepped up its military presence in the Arctic and High North.
Downing Street said they were sent at Denmark's request to join a reconnaissance group ahead of a planned Arctic Endurance exercise, but denied it amounted to a "deployment".
Denmark's defence minister, Troels Lund Poulsen, said on Wednesday an upcoming joint operation would involve several allied nations, warning that "no-one can predict what will happen tomorrow".
In a post on his Truth Social platform on Saturday, US time, Trump said he would impose tariffs of 10 per cent on eight European nations from February, increasing to 25 per cent in June.
"These Countries, who are playing this very dangerous game, have put a level of risk in play that is not tenable or sustainable," he wrote.
European Commission president Ursula von der Leyen and European Council president Antonio Costa said the EU stands in "full solidarity" with Denmark and the people of Greenland.
"Tariffs would undermine trans-Atlantic relations and risk a dangerous downward spiral. Europe will remain united, co-ordinated, and committed to upholding its sovereignty," they said.
With dpa
