In sharp exchanges before a NATO summit, US and French leaders trade barbs over future of the military alliance.

US President Donald Trump has launched an offensive on French President Emmanuel Macron for “very nasty” comments on NATO but the French leader said he stood by the remarks.

Trump also took aim at Germany’s perceived shortfall on defence funding commitments, but he singled out Macron before the two leaders met in London on Tuesday, in advance of a NATO summit marking 70 years of the military alliance.

Trump told reporters that Macron’s recent comments that NATO was suffering from “brain death” and lacked strategic leadership were “very, very nasty”.

“I think that’s insulting to a lot of different forces,” Trump said. “You just can’t go around making statements like that about NATO. It’s very disrespectful.”

Underlining the breadth of strife in a transatlantic bloc hailed by its backers as the most successful military alliance in history, Trump demanded that Europe pay more for defence and also make concessions to US interests on trade.

Trump later met Macron at Winfield House, a Grade II-listed neo-Georgian townhouse set in 12 acres (about 5 hectares) of grounds near London Zoo. The French president said that he stood by his assessment of the health of the alliance and lamented the US decision to withdraw troops from northern Syria in October.

The troop withdrawal effectively gave Turkey, a fellow NATO member, the green light to launch a military operation against Syrian Kurdish fighters, People’s Protection Units (YPG), who have long been US allies on the ground against ISIL (ISIS).

Turkey said it launched the operation to clear the border area of the Kurdish militias and establish a safe zone where it could relocate Syrian refugees.

Ankara considers the YPG as an extension of the Kurdistan Workers’ Party (PKK), which has fought the Turkish state for decades and is designated a “terrorist” organisation by Turkey, the US and EU.

Reporting afterwards from outside the ambassador’s residence where the meeting took place, Al Jazeera’s Jonah Hull said both leaders stuck to their positions.

“Donald Trump was lashing out in various directions, with the threat of further trade tariffs to be applied against France and the EU’s plan for a digital tax on US technologies companies, trade tariffs to be applied to try to extract from France and other NATO members yet more money for their collective defence,” he said.

“Mr Macron responded by saying he stood by his comments that NATO is on the verge of being ‘brain dead’ because of its inability to cooperate and coordinate amongst its members.

“Macron took particular aim at Donald Trump’s unilateralist policy in northern Syria, pulling US troops out, and then took aim at Turkey’s policy in northern Syria – condoned by the US – moving in and taking up arms against the Kurds. And also, of course, Mr Erdogan’s threat to undermine the collective security of NATO by standing in the way of the protection of the Baltic states against Russia, unless NATO falls into line and supports Turkey’s presence in northern Syria.”

Europe must ‘shape up’

Trump had referred to Macron’s “brain death” remarks when meeting NATO Secretary-General Jens Stoltenberg.

“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,” Trump told reporters.

Explicitly linking his complaint that Europe does not pay enough for NATO’s security missions to his staunch “America First” defence of US commercial interests, Trump said 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 tax on US technology giants.

The diplomacy flowed more easily when Trump met Canada’s Justin Trudeau. The pair discussed the North America trade deal between the US, Canada and Mexico. Trump said the deal was good for all three nations, calling it one of the few transactions in which all three countries benefit “as a unit against the world”.

But moving on to Germany, Trump dismissed recent signals from Berlin that it was ready to do more to match a NATO target of spending 2 percent of national output on defence.

Trump accused it and other nations which spend less than that target of being “delinquent”.

German Chancellor Angela Merkel said, despite all the differences between NATO members, she was heading into the summit “with optimism”.

Queen Elizabeth will on Tuesday evening host the leaders at Buckingham Palace. But even the British hosts, for generations among the most enthusiastic champions of the transatlantic partnership that NATO represents, are disunited over their project of quitting the EU and distracted by a rancorous election due next week.

“The question is, as we celebrate 70 years, are we waving in celebration or do people think we are drowning?” said a senior European NATO diplomat.