The FBI is investigating Donald Trump's former top counter-terrorism official, who resigned from his role earlier this week, over alleged leaks, sources have told CBS News, the BBC's US partner.

Joe Kent is under investigation in connection with alleged leaks of classified information, with sources telling CBS that the probe began before his departure as US National Counterterrorism Center director.

Announcing his resignation on Tuesday, Kent stated he could not support the war in Iran in good conscience and that the country posed no imminent threat to the US - a claim fiercely contested by the White House.

The FBI's criminal division is handling the investigation, which may have been underway for some time, according to informed sources.

In the aftermath of Kent's resignation, former deputy White House chief of staff Taylor Budowich described Kent as being often at the center of national security leaks but declined to elaborate on specific incidents.

Kent's resignation letter explicitly cited pressure from Israel and its American lobby as influencing the decision to engage in the war against Iran, prompting the Anti-Defamation League to criticize the letter for perpetuating harmful antisemitic tropes.

During a podcast appearance, Kent reiterated his stance that the military action against Iran was unwarranted, suggesting there had been no substantial evidence of an imminent threat from Iran or that the country was on the brink of acquiring nuclear capability.

Both Kent and former President Trump have remarked on the circumstances, with Trump indicating that he always perceived Kent's approach to security as inadequate.

As the political and national security landscape continues to evolve, Kent's allegations and the ongoing investigation highlight the complexities of governance, military decisions, and public accountability.