The US president has plunged the alliance into chaos with his threat to withdraw from Nato.

Donald Trump has come close to suggesting that the United States might unilaterally exit from Nato if other member states failed to dramatically increase their spending on the military bloc.

He plunged the summit into chaos on Thursday by saying that the US would “go it alone”, if European states failed to boost their spending to at least 2% by January.

The summit is shaping up to be one of the most difficult alliance gatherings in years as Trump continues to pressure NATO allies to increase their military spending.

Trump has repeatedly criticized alliance members for their levels of defense spending ahead of the meeting.

At an emergency press conference, Trump later appeared to row back from this threat, claiming that Nato members had agreed to commit an extra $33bn (£25bn). He said it was “a little tough for a little while” and that he had told the Europeans he would be “very unhappy” if they did not up their spending “substantially”.

Reporters then asked the President if he sees Putin as a friend or foe, and he responded by describing Putin as a “competitor.”

“I really can’t say right now. As far as I’m concerned, a competitor. A competitor. I think that getting along with Russia, getting along with China is a good thing, getting along with others is a good thing. It’s not a bad thing, I’ve said that many times,” Trump said.

Also, President Trump on Thursday waded into the U.K. battle over Brexit, casting doubt on Prime Minister Theresa May’s approach to leaving the European Union by suggesting it’s not what Brits voted for.

Before departing for London, he told reporters in Brussels amid a summit with NATO leaders that “it’s not for me to say” what Britain should do. But later in his remarks, he indicated that he didn’t agree with the current approach.

“I would say Brexit is Brexit…the people voted to break it up,” Trump said. “So I would imagine … that’s what they’ll do but maybe they’re taking a bit of a different route. So I don’t know if that’s what they voted for.” 

But, he added, a “tremendous amount of progress” had been made. Nato was now “much stronger”, he added, with spending “rocketing” upwards.

Before his departure for NATO summit, US president Donald Trump said that it is not fair to the U.S. taxpayers to spend for NATO expenses but European Council President Donald Tusk hits back by saying that Washington has no better ally than the EU.

This week’s two-day summit, began on Wednesday at Nato’s new HQ in the Belgian capital, is expected to be dominated by US demands for increased spending by other members of the 29-nation alliance.