The Trump administration's top official on counterterrorism has resigned from his position, citing opposition to the war in Iran, and urged the president to "reverse course".

In a letter posted on Tuesday to his X account, National Counterterrorism Center Director Joe Kent said that Iran posed "no imminent threat" to the US and claimed that the Trump administration "started this war due to pressure from Israel and its powerful American lobby".

Kent, 45, is a US special forces and CIA veteran whose wife, navy cryptologic technician Shannon Kent, was killed in a suicide bombing in Syria in 2019.

The White House has dismissed the letter as having "many false claims" about Iran.

Speaking in the Oval Office on Tuesday, Trump said that he thought Kent was a "nice guy" but "weak on security".

Trump said that Kent's resignation letter made him realise "it was a good thing that he's out" and that he disagreed with Kent's assessment of the Iranian threat.

With his departure, Kent becomes the most high-profile figure from within the Trump administration to publicly criticise the US-Israeli operation in Iran.

In the letter, Kent said that had previously supported Trump's foreign policy platform and until last year believed that he had "had understood that the wars in the Middle East that robbed America of the precious lives of our patriots and depleted the wealth and prosperity of our nation."

Additionally, Kent alleged that "high-ranking Israeli officials" and influential US journalists had sowed "misinformation" that caused Trump to undermine his "America First" platform.

"This echo chamber was used to deceive you into believing that Iran posed an imminent threat to the United States," the letter continued. "This was a lie."

Kent, a long-time supporter of Trump's who unsuccessfully ran for Congress twice, was nominated by the president early in his administration and narrowly confirmed to his post, with many Democrats criticising his links to extremist groups including members of the Proud Boys.

In the confirmation hearing, Kent also refused to back away from claims that federal agents had fomented the January 6 riots at the US Capitol or that Trump had won the 2020 election.

At the National Counterterrorism Center, he reported to Director of National Intelligence Tulsi Gabbard and oversaw the analysis and detection of potential terrorist threats from around the globe.

Previously, Kent had deployed 11 times overseas with the US military, including with the US Army's special forces in Iraq.

He later became a paramilitary officer at the CIA, before leaving government service after his wife's death.

Kent cited his military service and her death in his letter, saying that he "cannot support sending the next generation off to fight and die in a war that serves no benefit to the American people nor justifies the cost of American lives".

White House Press Secretary Karoline Leavitt said that Kent's suggestion that "Trump made the decision based on the influence of others, even foreign countries, is both insulting and laughable".

"As President Trump has clearly and explicitly stated, he had strong and compelling evidence that Iran was going to attack the United States first," she added.

In a brief interview with the New York Times, conservative media commentator Tucker Carlson praised Kent, with whom he has close personal ties.

"Joe is the bravest man I know, and he can't be dismissed as a nut," Carlson said. "He's leaving a job that gave him access to the highest-level relevant intelligence. The neocons will try to destroy him for that."

"He understands that and did it anyway," he added.

There have been a number of resignations among senior officials in the Trump administration, including Security and Exchange Commission enforcement director Margaret Ryan and Kennedy Center President Ric Grenell.

The president's second term, however, has seen far less turnover than his previous tenure at the White House between 2017 and 2021.