US intelligence officials were sceptical of an alleged Iranian assassination threat against Donald Trump that was relayed by Israel, sources told The Washington Post.

The threat was relayed by the Israeli government to the CIA, but analysts had doubts about the credibility of the information and conveyed their thoughts to the Trump administration, one official indicated.

Another official described the reports of threats against the US president's life as "Israeli-derived, not U.S.-generated, and viewed as low confidence".

Earlier, The Washington Post broke the story that Trump secretly left Ankara on the military aircraft amid an alleged Iranian assassination threat.

The latest report follows confirmation of Trump secretly leaving Turkey on a military aircraft, instead of an Air Force One jumbo jet he was seen on television boarding.