Trump on Theresa May's Brexit plan: 'I don't know if that's what they voted for'

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.” 

“I just want the people to be happy and they’re great people,” he said before adding: "I don't know what's going on with the negotiations. Who knows?"

His remarks came shortly before he flew to London for a three-day working visit, where he will meet with both May and Queen Elizabeth II. 

Trump made reference to the protests due to be held in London on Friday.  

“There might be protests but...I think those people they like me a lot and they agree with me on immigration. I think that’s why you had Brexit in the first place, because of immigration,” he said.

BORIS JOHNSON QUITS AS UK FOREIGN SECRETARY, LEAVING MAY'S GOVERNMENT ON BRINK OVER BREXIT

May, meanwhile, is fighting for her political life after the resignation of Foreign Secretary Boris Johnson and Brexit Secretary David Davis this week in protest of her latest Brexit plan — which critics say is too soft and will lead to Britain being a “colony” of the E.U. 

The high-profile resignations were sparked by May demanding cabinet members support a plan for Brexit that would include Britain partly remaining in the single market and signing up to a "common rulebook" for goods. 

Johnson, a vocal backer of Trump, suggested May was surrendering to Brussels. 

"It is as though we are sending our vanguard into battle with the white flags fluttering above them," he wrote in his resignation letter. 

Trump has since praised Johnson and suggested he will talk to the former foreign secretary while in London. 

“I like him,” Trump said of Johnson Tuesday. “Boris Johnson is a friend of mine.” 

When asked whether May would remain in power, the president responded: “That’s up to the people—not up to me.” 

Fox News’ Brooke Singman contributed to this report.

Adam Shaw is a reporter covering U.S. and European politics for Fox News.. He can be reached here.