Donald Trump has declared that Nato is no longer "obsolete" in a massive u-turn which could fuel fears surrounding relations between the US and Russia.
In the past the President had been hugely critical of the alliance, which has been in existence since 1949. He has repeatedly questioned its purpose and demanded the United States scale back how much it pays to the bloc.
The comments came as he was hosting Nato Secretary General Jens Stoltenberg at the White House in Washington DC.
The President revealed the discussions had shown him how important the alliance was to combat terrorism, and said Nato had made a change he had previously requested.
However Mr Trump maintained that some Nato members are not presently making a fair contribution and called on them to do so.
His latest comments are likely to fuel worries surrounding the rising tension between Moscow and Washington following last week's chemical attack on the Syrian town of Khan Sheikhun.
The US launched an airstrike on Syria in response to the street and Mr Trump has said relations between the two countries are at an "all-time low."