The man who claims he killed Osama bin Laden is backing President Trump's contentious decision to restore the rank of Eddie Gallagher - the Navy SEAL demoted after being convicted of posing with the corpse of an Iraqi civilian.

In an interview on Monday, Robert O'Neill, the Navy SEAL crediting with shooting bin Laden during the 2011 raid on his Abbottabad compound, also hit out at 'whiny' Pentagon officials, some of whom are said to be angered over the President's intervening in military affairs.

Speaking with The Washington Examiner, O'Neill stated: 'Everyone knows Gallagher will always be a SEAL... they'll never be able to take that away from him'.

He added: 'It's a special designation. SEALs go through the hardest training in the world… basically beating you up. It turns you into a special warrior'.

Trump reportedly ordered that Gallagher be able to keep his prestigious 'Trident'' pin - effectively allowing him to be able to retire as a SEAL.

Robert O'Neill (left) has defended Trump's decision to restore the rank of Navy SEAL Eddie Gallagher (right) after he was demoted following a high-profile military trial earlier this year, during which he was accused of war crimes

US Navy Secretary Richard Spencer, who was fired from his position on Friday, publicly disagreed with that decision.

Angered by Trump's interference in disciplinary matters, Spencer wrote a stinging letter, which read: '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.'

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

Gallagher faced a court martial trial earlier this year after being accused of war crimes, including stabbing a captured ISIS prisoner to death with a hunting knife.

However, Gallagher was acquitted on almost all charges in, but was found guilty of posing for a photograph with a corpse and was subsequently demoted.

O'Neill, the Navy SEAL who claims he shot bin Laden during the 2011 raid on his Abbottabad compound, is pictured with President Trump

O'Neill (right) told The Washington Examiner: 'Everyone knows Gallagher (left) will always be a SEAL... they'll never be able to take that away from him'

However, on November 15, Trump 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 (Sea, Air, and Land) 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.

On Monday, Trump continued to defend his decision on Gallagher, stating: 'I think what I'm doing is sticking up for our armed forces. And there's never been a president that's going to stick up for them and has like I have'.