In an interview with Fox News aired on Thursday, Trump appeared unaware that 457 British soldiers were among NATO troops who died during the conflict in Afghanistan following the September 11, 2001, attacks on the United States.

"They'll say they sent some troops to Afghanistan," Trump told the US outlet, referring to NATO allies.

"And they did, they stayed a little back, a little off the front lines," he added, triggering outrage across the political divide in Britain.

Trump also repeated his suggestion that NATO would not come to the aid of the US if asked to do so.

In fact, following the 9/11 attacks, the UK and several European countries joined the US in Afghanistan after it invoked NATO's collective security clause for the first and only time.

Soldiers from Canada, France, Germany, Italy, Denmark and others also died in the conflict.

"Let me start by paying tribute to 457 of our armed services who lost their lives in Afghanistan," Starmer said in a video message.

"There are many also who were injured, some with life-changing injuries, and so I consider President Trump's remarks to be insulting and frankly, appalling, and I'm not surprised they've caused such hurt to the loved ones of those who were killed or injured."

He said that if he had misspoken in such a way, he "would certainly apologise".

The White House rejected Starmer's comments and defended the president.

"President Trump is absolutely right - the United States of America has done more for NATO than any other country in the alliance has done combined," Taylor Rogers, a White House spokeswoman, said in a statement sent to AFP.

- 'Heroes' -

Poland's Defence Minister Wladyslaw Kosiniak-Kamysz said he expected respect for Polish veterans "who have proven how much they serve this country and our commitments to allies".

Poland lost 43 soldiers in the conflict in Afghanistan.

French armed forces minister Catherine Vautrin said 90 French soldiers died in Afghanistan on operations alongside NATO allies and "many others" were wounded.

"We remember their sacrifice, which commands respect."

UK defence minister John Healey posted on X that the British troops who died were "heroes who gave their lives in service of our nation".

UK Armed forces minister Al Carns, who served five tours in Afghanistan, said Trump's comments were "utterly ridiculous".

The leader of the opposition Conservatives, Kemi Badenoch, said Trump's comments were "complete nonsense" which could weaken the NATO alliance.

Even Nigel Farage, leader of the anti-immigration Reform UK party and a long-time Trump supporter rebuked the American leader.

"Donald Trump is wrong," he said on X. "For 20 years our armed forces fought bravely alongside America's in Afghanistan."

Lucy Aldridge, whose son William died aged 18 in Afghanistan, told The Mirror newspaper that Trump's remarks were "extremely upsetting".

Mark Atkinson, Director General of the veterans' charity, The Royal British Legion, said the service and sacrifice of British troops in Afghanistan "cannot be called into question".

Prince Harry, who undertook two frontline tours to Afghanistan with the Army Air Corps, also weighed in.

"I served there. I made lifelong friends there. And I lost friends there," he said.

"Thousands of lives were changed forever. Mothers and fathers buried sons and daughters. Children were left without a parent. Families are left carrying the cost. Those sacrifices deserve to be spoken about truthfully and with respect."

According to official UK figures, 405 of the 457 British casualties who died in Afghanistan were killed in hostile military action.

The US reportedly lost more than 2,400 soldiers.

More than 150,000 UK armed forces personnel served in Afghanistan between September 2001 and August 2021, the Ministry of Defence said, making the UK the second-largest contributor to the US-led force there.