Veterans from across Europe hit back at US President Donald Trump's suggestion that they had stayed "a little off the front lines" in Afghanistan, saying on Friday that hundreds of their comrades had died fighting alongside American forces.

Senior politicians joined the criticism, with the British prime minister's office saying Trump had been "wrong to diminish the role of Nato troops" during two decades of war.

Trump told Fox News on Thursday the United States had "never needed" the transatlantic alliance and accused allies of staying "a little off the front lines" in Afghanistan.

His remarks added to already strained relations with European allies after he used the World Economic Forum in the Swiss ski resort of Davos to again signal his interest in acquiring Greenland.

"We expect an apology for this statement," Roman Polko, a retired Polish general and former special forces commander who served in Afghanistan and Iraq, told Reuters in an interview.

Trump has "crossed a red line", he added. "We paid with blood for this alliance. We truly sacrificed our own lives."

Britain's veterans minister, Alistair Carns, whose own military service included five tours including alongside American troops in Afghanistan, called Trump's claims "utterly ridiculous".

"We shed blood, sweat and tears together. Not everybody came home," he said in a video posted on X.

Stuart Tootle, a retired British colonel who commanded the first British battle group sent to Helmand, Afghanistan's largest province, in 2006, said Trump should apologise.

He also said that while he had "some sympathy" for Trump's criticism of what he described as under-investment in Nato by Britain and other Western European nations, he had none for the president's "really unfortunate, inaccurate and totally unjustified" remarks.

Some politicians noted that Trump had avoided the draft for the Vietnam War, citing bone spurs in his feet.

"Trump avoided military service 5 times," Ed Davey, leader of Britain's centrist Liberal Democrats, wrote on X. "How dare he question their sacrifice."

Poland's sacrifice "will never be forgotten and must not be diminished", Defence Minister Wladyslaw Kosiniak-Kamysz said.

"Poland is a reliable and proven ally, and nothing will change that," he said on X.

Trump's comments were "ignorant", said Rasmus Jarlov, an opposition Conservative Party member of Denmark's parliament.

The United States lost about 2,460 troops in Afghanistan, according to the US Department of Defense.

A total of 457 British military personnel were killed from the more than 150,000 who were deployed.

More than 150 Canadians were also killed along with 90 French service personnel, while Denmark – which has been under heavy pressure from Trump to sell its semi-autonomous region of Greenland to the US – lost 44 troops, one of Nato's highest per-capita death rates. (Reuters)