Sir Keir Starmer has held a call with Donald Trump over the president's "wrong" decision to implement tariffs on several European countries including Britain.
The US President has vowed to implement a wave of increasing tariffs until America is allowed to purchase Greenland.
Mr Trump announced his plans in a lengthy post to his Truth Social yesterday.
Sir Keir held a flurry of calls on the matter this afternoon, including with the US president, No10 said.
A Downing Street spokeswoman said: "The Prime Minister had a number of calls with leaders this afternoon.
"He spoke to Prime Minister of Denmark, Mette Frederiksen; President of the European Commission, Ursula von der Leyen and Nato Secretary-General Mark Rutte. He then spoke to President Trump.
"In all his calls, the Prime Minister reiterated his position on Greenland. He said that security in the High North is a priority for all Nato allies in order to protect Euro-Atlantic interests.
“He also said that applying tariffs on allies for pursuing the collective security of Nato allies is wrong.”
The two leaders spoke over the phone this afternoon, No10 has confirmed
| PAIn a joint message earlier today, Denmark, Finland, France, Germany, the Netherlands, Norway, Sweden and the UK said the tariff threats "risk a dangerous downward spiral".
The statement read: "We stand in full solidarity with the Kingdom of Denmark and the people of Greenland.
"Tariff threats undermine transatlantic relations and risk a dangerous downward spiral.
"We will continue to stand united and coordinated in our response. We are committed to upholding our sovereignty.
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"As members of Nato, we are committed to strengthening Arctic security as a shared transatlantic interest."
The US President said 10 per cent tariffs would come into effect for each of the European countries that issued the statement from February 1, and increase to 25 per cent from June 1, until America reaches a deal "for the complete and total purchase of Greenland".
He wrote to Truth Social: "Starting on February 1, 2026, all of the above mentioned countries (Denmark, Norway, Sweden, France, Germany, The United Kingdom, The Netherlands, and Finland), will be charged a 10 per cent tariff on any and all goods sent to the United States of America.
"On June 1, 2026, the tariff will be increased to 25 per cent.
Donald Trump announced a wave of increasing tariffs in a post to Truth Social yesterday
|REUTERS
"This tariff will be due and payable until such time as a deal is reached for the complete and total purchase of Greenland."
Mr Trump appeared to take issue with a Danish-led military exercise conducted with allies in Greenland this week, saying the countries had “journeyed to Greenland, for purposes unknown”.
Downing Street previously confirmed that one UK military officer had been sent to Denmark at the country's request to join a reconnaissance group ahead of a planned Arctic Endurance exercise, but denied it amounted to a “deployment”.
President Trump has repeatedly said Greenland is vital to US security due to its strategic location and large mineral deposits and has not ruled out using force to take it.
Greenland and Denmark have said the island is not for sale.
Protests were held in Denmark and Greenland on Saturday in opposition to Mr Trump's plans.
In Copenhagen, demonstrators chanted "Greenland is not for sale" and held up slogans such as "No means No" and "Hands off Greenland" alongside the territory's red-and-white flag as they marched to the US embassy.