US President Donald Trump said in an interview with The Washington Post that he does not want the United States to leave NATO, but that America's allies have to pay their share.

"I had some that were paying almost nothing, and now they're paying. And they asked me the big question: Would you leave if — and I said, 'Yeah, I would leave'. And if you don’t give that answer, they're not going to pay", the US president said, as quoted by the media outlet.

When asked whether he really wanted the US to exit NATO, Trump said, "No, I don't want to leave ... But I want them to pay their fair share".

NATO states agreed in the Brussels Summit Declaration, signed in July 2014, to raise their defence spending to 2 percent of their respective GDP figures by 2024, something that a lot of Washington's allies have struggled to achieve.

Former White House National Security Adviser John Bolton has claimed in his recent book, "The Room Where It Happened", that Trump wanted to threaten NATO leaders at the 2018 summit with US withdrawal from the alliance if they did not pay 2 percent of their GDP.

According to the former adviser, he and US Secretary of State Mike Pompeo decided to convince the president to stay in the bloc, but, possibly reduce US contributions. Eventually, Trump did as Bolton advised him — declared his support for NATO — but criticised those member states that still had small defence budgets.