THE FBI HAS opened an investigation into a senior US counterterrorism official who quit in protest of the Iran war for allegedly leaking classified information, US media have reported.

Joseph Kent served as director of the National Counterterrorism Center (NCTC) until his resignation on Tuesday, writing to President Donald Trump that he could not “in good conscience support the ongoing war in Iran.”

“Iran posed no imminent threat to our nation, and it is clear that we started this war due to pressure from Israel and its powerful American lobby,” said Kent (45), a former special forces member.

The FBI investigation into Kent predated his departure, according to reports by outlets including the New York Times and CBS, both citing unnamed sources with knowledge of the situation.

A source told news website Semafor that the investigation was “months-long”.

The FBI did not immediately respond to a request for comment.

Kent was once a Trump ally and was appointed by the Republican president to head the NCTC, where he worked under Tulsi Gabbard to analyse and coordinate the US response to terrorist threats and served as the principal counterterrorism adviser to the president.

On Tuesday, Trump accused Kent of being “very weak on security” and said it’s a “good thing that he’s out.”

White House Press secretary Karoline Leavitt pushed back against what she called “false claims” in Kent’s resignation letter, calling “insulting and laughable” the suggestion that the decision to go to war was made “based on the influence of others.”

“As President Trump has clearly and explicitly stated, he had strong and compelling evidence that Iran was going to attack the United States first,” Leavitt said.