London: US President Donald Trump on Tuesday took aim at President Emmanuel Macron over the French leader’s criticism of Nato, and criticised the other members of the military alliance for being too slow to beef up their defence budgets.

As prime ministers and presidents of the 29-member alliance converged on London to mark Nato’s 70th birthday, Trump told reporters Macron’s comments were “very, very nasty” when he lamented the “brain death” of the organisation due in large part to a lack of US leadership.

“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.”

During campaigning for the last election, Trump described Nato as “obsolete”. He has since tempered his criticism somewhat.

Macron was angered when Trump unilaterally pulled troops out of northern Syria last month, a move that Turkey saw as a green light for an invasion. The European Union is mired in a political crisis sparked by its inability to manage Syrian refugee arrivals, and fears that more people might flee.

Relations between the US and France are also particularly strained this week after the US Trade Representative proposed introducing tariffs on .4 billion (Dh8.8 billion) in goods in retaliation for a French tax on global tech giants. Trump and Macron are due to meet on the sidelines of the summit.

Discussing military funding, Trump insisted that “a lot of countries haven’t paid”. After Russia annexed the Crimean Peninsula in 2014, Nato countries halted their post-Cold War spending cuts and began increasing spending. They pledged to “move toward” spending 2 per cent of GDP on their national defence budgets by 2024.

Trump also said things would get very tough with the European Union unless the bloc shapes up over trade and Nato. “The European Union [is] treating the United States very, very unfairly on trade,” Trump said at a meeting with the head of Nato.

“The deficit for many, many years has been astronomical with the United States and Europe in their favour. I’m changing that and I’m changing it very rapidly. 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. We’re talking to the European Union about trade and they have to shape up or otherwise things are going to get very tough.”