Donald Trump has again attacked Nato for not supporting the US in the Iran war, following a private meeting with its Secretary General Mark Rutte at the White House.

In a post shared to Truth Social after the meeting, the US President said: "NATO WASN'T THERE WHEN WE NEEDED THEM, AND THEY WON'T BE THERE IF WE NEED THEM AGAIN."

Meanwhile, Rutte has described his meeting to CNN with Trump as "very frank" and "very open", despite clear disagreements.

Ahead of the talks on Wednesday, Trump had toyed with the idea of quitting the trans-Atlantic military alliance after several Nato countries resisted his calls to help reopen the Strait of Hormuz to ease rising global oil prices.

The White House did not disclose details of the talk.

The Secretary General was at the White House for over two hours on Wednesday, although it is unknown how long the meeting with Trump was.

The meeting was expected to cajole and convince Trump that it's in his interest, and America's, to stay in the Nato alliance.

What is clear, however, is that Trump still has deep misgivings about the alliance and the member countries that he believes did not help the US enough before and during Operation Epic Fury.

In recent weeks, Trump has threatened to withdraw from the 32-member transatlantic alliance.

Asked about Nato's role in the ongoing conflict with Iran, White House Press Secretary Karoline Leavitt on Wednesday said in a direct quote from the president that Nato was "tested and they failed".

Leavitt said Nato countries had "turned their backs on the American people," who fund their nations' defense, and that Trump would have a "very frank and candid conversation" with the Nato chief.

Meanwhile, much of Rutte's message to Trump appears to be that many European countries did not stand in the way.

The Secretary General told CNN that he pointed out that "the large majority of European nations has been helpful with basing, with logistics, with overflights".

"It's therefore a nuanced picture," Rutte said.

Whether or not that point - and the Secretary General's own warm relationship with Trump - are enough for the US president remains to be seen.

Asked if the world was safer now than it was before the war, Rutte said "absolutely" and credited that to Trump's "leadership" in degrading Iran's nuclear threats.

He added Nato members do not see the war in Iran as illegal, and most agreed it was important to degrade Iran's nuclear capabilities.

At the end of 2023, the US Congress did vote to prohibit any US president from unilaterally withdrawing from Nato without the approval of a two-thirds Senate majority or an act of Congress.

The relationship between the administration and the Nato alliance was already in a difficult place before the war with Iran, largely as a result of disagreements over Trump's plans for Greenland.

Trump included his frustrations over Greenland in his Truth social post after the meeting with Rutte, by saying: "REMEMBER GREENLAND, THAT BIG, POORLY RUN, PIECE OF ICE!!!"

The conflict in Iran, however, has taken Trump's grievances with Nato to new heights and created what is perhaps the greatest challenge the alliance has faced in its history.