WASHINGTON — The chief of the US Navy on Sunday criticised Donald Trump after being sacked in a dispute over an elite SEAL commando whose demotion for misconduct was reversed by the president.

Richard Spencer was ousted as Navy Secretary, a civilian position, in a case that has fueled reports of anger among US military leadership over Trump's interference in discipline cases.

"I no longer share the same understanding with the Commander in Chief who appointed me, in regards to the key principles of good order and discipline," Spencer said in a stinging letter published by US media.

"I hereby acknowledge my termination as United States Secretary of the Navy."

The dispute centres on the fate of Navy SEAL Edward Gallagher who was accused of war crimes in a high-profile case but was found guilty of a lesser offense.

On November 15, Trump – the commander-in-chief of the US military – reversed the demotion handed down to Gallagher.

Trump tweeted on Sunday that Gallagher had been "treated very badly" by the navy, and that Spencer had been asked to resign over the issue and over his alleged failure to address budget overruns.

The president said Gallagher would not be expelled from the elite SEAL force.

"Eddie will retire peacefully with all of the honors that he has earned," Trump tweeted.

Defense Secretary Mark Esper said he had asked for Spencer's resignation "after losing trust and confidence in him regarding his lack of candor over conversations with the White House," the Department of Defense said in a statement.

Esper said he was "deeply troubled by this conduct". — AFP