The rift between the United States and NATO that has been widening ever since President Donald Trump returned to the White House stretched further this week when the two sides sat down for a meeting aimed at repairing damage.

After talking in Washington on Wednesday with NATO Secretary-General Mark Rutte, Trump took to social media to blast the Western military alliance that the US has effectively led since 1949.

"NATO wasn't there when we needed them, and they won't be there if we need them again," he wrote in block capitals.

The US president has made similar claims before — saying NATO should have joined its strikes on Iran, even though the alliance is a defensive one, not offensive, and is aimed at ensuring members are on hand to help a peer that has been attacked.

Rutte told the US broadcaster CNN his meeting with Trump was "very frank", but, instead of focusing on NATO's defensive mandate, he said "the large majority of European nations have been helpful with basing, with logistics, with overflights".

"It's therefore a nuanced picture," he added.

Greenland bid

The row over whether NATO should have done more to help the US and Israel in their attacks on Iran follows earlier disputes between Washington and the military alliance, including a protracted standoff in which Trump said the US wanted Greenland, even though it belongs to NATO member Denmark and is not up for grabs.

The Trump administration has also berated NATO member nations for not spending enough of their GDP on their militaries.

White House Press Secretary Karoline Leavitt said on Wednesday that the president had told her that NATO had been "tested and they failed".

The disputes have led Trump to threaten to take the US out of the 32-member trans-Atlantic alliance.

But experts say Europe was right to avoid full participation in the war.

Koert Debeuf, a distinguished adjunct professor in Middle East studies at the Brussels School of Governance, told China Daily: "European countries have all made clear that this is not their war. If they choose to assist countries such as Saudi Arabia, the United Arab Emirates, or Qatar, they would only do so after the war ends. For now, no European country wants to be involved, and that is unlikely to change."

While some European leaders, including the prime minister of Spain and the president of Germany, have said the attacks on Iran are likely illegal under international law, most have remained largely silent, Debeuf explained, which he said reflects "deep discomfort with the situation".

"What is clear is that this is widening the gap between the United States and Europe in the short term," he added.

Ondrej Dostal, a member of the European Parliament from Czech Republic, told China Daily that Europeans should have reservations about the war.

"In recent days, President Trump has unleashed a series of disgusting tweets, openly threatening to exterminate a whole civilization, to send Iran to the 'Stone Age'," Dostal said.

He also used other insulting words when addressing Iranians, Dostal said.

"Europe must clearly and unequivocally reject this."

Dostal said Europe has bowed to the Trump administration on every occasion, through the unequal EU-US trade deal, its abuses of Cuba and Venezuela, and its illegal attack on Iran, and "this must end now".

"We must be clear: it was the tacit acceptance by the entire European establishment of US hegemonic aspirations that has led to the catastrophe in Iran. Had Europe stood its ground in defending international law and the UN Charter, much could have been prevented."