US President Donald Trump has blasted his French counterpart Emmanuel Macron for calling NATO “brain dead”.

Mr Trump then clashed with the French president about accepting captured ISIS fighters, as a heated dispute between the two world leaders erupted at the North Atlantic Treaty Organization summit in London.

The icy exchange reflected an apparent rift between the French and US presidents over the future of the NATO alliance and how to deal with the nearly 10,000 prisoners held in Syria.

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It all began when Mr Macron said in a previous interview last month that NATO was suffering “brain death” because of America’s lack of commitment to the trans- Atlantic alliance which he argued had been made worse under the Trump administration.

On Tuesday, Mr Macron refused to back down, saying in a news conference “I know that my statements created some reaction,”  but “I do stand by [them]”.

“It’s a tough statement, though, when you make a statement like that, that is a very, very nasty statement to essentially 28, including them, 28 countries,” Mr Trump told reporters as he met the head of NATO in London on Tuesday.

Mr Macron then schooled Mr Trump when it came to his assertion that ISIS fighters are mostly European.

When Mr Trump questioned whether France will welcome back terrorists captured in Syria and Iraq, he responded saying “Let’s be serious”.

“The very large numbers of fighters you have on the ground are the fighters coming from Syria, from Iraq and the region,” Mr Macron said.

ISIS fighters with European backgrounds are “a tiny minority of the overall problem,” he added.

The pair again clashed when asked about their views on how NATO members should interact with Russia.

“I think we get along with Russia”, Mr Trump said, while Mr Macron that while it is “important to have a strategic dialogue with Russia,” leaders “must do so without naïveté”.

The leaders of Canada and the Netherlands added their support on Tuesday to a Franco-German proposal to reform NATO.

“I don’t think you survive 70 years as an alliance without regularly reflecting,” Canadian Prime Minister Justin Trudeau told a forum before the summit, sitting alongside his Dutch counterpart Mark Rutte.

Mr Trump explicitly linked his complaint that Europe does not pay enough for NATO’s security missions to his “America First” defence of US commercial interests, saying it was time for Europe to “shape up” on both fronts.

“It’s not right to be taken advantage of on NATO and also then to be taken advantage of on trade, and that’s what happens. We can’t let that happen,” he said of transatlantic disputes over everything from the aerospace sector to a European “digital tax” on US technology giants.

Dismissing signals from Germany that it would do more to hit a NATO target of spending 2 per cent of national output on defence, Mr Trump accused it and other nations of being “delinquent”.

NATO Secretary-General Jens Stoltenberg, who shared omelette and sausages with Mr Trump over breakfast, tweeted that the pre-summit talks had got off to an “excellent start”.

-with agencies