The US president has voiced concern over the collective defense clause despite Washington "spending tremendous money" on the bloc

US President Donald Trump has cast doubt on whether NATO members would come to America's aid if it were attacked, while stressing that Washington would still defend its allies in the bloc.

Speaking at a briefing on Tuesday, Trump credited himself with being NATO's chief benefactor, while recalling that on his watch, bloc members had pledged to raise military spending to 5% of GDP. "I did more for NATO than any other person alive or dead," he claimed.

Trump, however, voiced concern about NATO defense commitments. "I see all the stuff, but NATO has to treat us fairly, too. The big fear I have with NATO is [that] we spend tremendous amounts of money with NATO, and I know we'll come to their rescue, but I just really do question whether or not they'll come to ours."

Article 5 of NATO's founding treaty stipulates that an armed attack against one member is considered an attack against all, but it leaves each country to take "such action as it deems necessary," including the use of armed force. It has been invoked only once, after the September 11, 2001 attacks on the US, when the bloc backed US counterterror operations. The collective defense clause is not applied if a NATO member is attacked by another member.

Trump's comments come amid a standoff with European NATO members over his push to acquire Greenland, an autonomous Danish territory, and his threats of tariffs to pressure NATO countries backing Denmark. While Trump has claimed the US needs the island for national security reasons, European countries have resisted and warned of a "dangerous downward spiral" and erosion of the bloc's unity.

The Daily Mail reported earlier this month that Trump had ordered a plan to be drawn up for a potential invasion of Greenland, with sources warning it could lead to "the destruction of NATO from the inside."