Washington, United States — US President Donald Trump's National Security Advisor Mike Waltz is to leave his post following a scandal in which a journalist was accidentally included on a chat between officials about air strikes on Yemen, US media reported.

Waltz and his deputy Alex Wong were both set to leave, CBS News reported, while Fox News said Trump was expected to comment on the matter soon. 

The former US congressman is the first major official to leave the administration in Trump's second term, which has so far been more stable in terms of personnel than his first.

A White House official did not confirm the reports, saying they "do not want to get ahead of any announcement."

Waltz had been under pressure since the editor-in-chief of the Atlantic Magazine revealed in March that Waltz had mistakenly added him to a chat on the commercial messaging app Signal about attacks on Huthi rebels.

Officials on the chat laid out the attack plan including the timings that US warplanes would take off to bomb targets in Yemen, with the first texts barely half an hour before they launched.

Defense Secretary Pete Hegseth has also faced pressure over the scandal.

"1215et: F-18s LAUNCH (1st strike package)", Hegseth wrote in one text, referring to F/A-18 US Navy jets, before adding that "Target Terrorist is @ his Known Location so SHOULD BE ON TIME."

"1415: Strike Drones on Target (THIS IS WHEN THE FIRST BOMBS WILL DEFINITELY DROP, pending earlier 'Trigger Based' targets)."

A short time later, Waltz sent real-time intelligence on the aftermath of an attack, writing that US forces had identified the target "walking into his girlfriend’s building and it’s now collapsed."