The comments come as top U.S. officials increasingly voice frustration with their NATO allies over their refusal to join the U.S.-Israeli war with Iran.
Asked by the Telegraph whether he would reconsider the U.S. membership in the alliance after the war, Trump said: "Oh yes, I would say (it's) beyond reconsideration.
The U.S. president, a long-time critic of the alliance, went on to call NATO a "paper tiger" and said Russian President Vladimir Putin shares that opinion.
Trump also noted that the U.S. has "been there" for the alliance when it came to the Russia-Ukraine war.
Matthew Whitaker, the U.S. ambassador to NATO, said Trump is also reevaluating U.S. "support for the European efforts in Ukraine" in light of recent events.
Finland's President Alexander Stubb later said he held a "constructive discussion and exchange of ideas on NATO, Ukraine, and Iran" with the U.S. leader.
Under pressure from Trump, all NATO members met the 2% of GDP defense spending goal last year and agreed to raise that benchmark to 5%. »