WASHINGTON (PTI): In a rare move, US Defence Secretary Mark Esper has fired Navy chief Richard Spencer over his handling of a Navy SEAL's case that has pitted military leaders against President Donald Trump.

The case is related to Edward Gallagher, who was convicted for posing with a corpse in Iraq in 2017. For that Gallagher was demoted, but President Trump later reinstated his rank.

Tump intervened in his case and issued a pardon on November 15. Trump has drawn criticism from parts of the military after pardoning army officers convicted of war crimes.

Esper on Sunday said he lost confidence in Spencer after finding out the navy chief had tried to end the dispute behind his back.

"I am deeply troubled by this conduct shown by a senior DOD (Department of Defence) official," Esper said in a statement.

"Unfortunately, as a result I have determined that (Navy) Secretary Spencer no longer has my confidence to continue in his position. I wish Richard well," he said.

According to Pentagon spokesman Jonathan Hoffman, the Defence Secretary asked for the resignation of Spencer after losing trust and confidence in him regarding his lack of candour over conversations with the White House involving Gallagher.

Esper and Chairman of the Joint Chiefs of Staff Chairman Mark Milley spoke with President Donald Trump on Friday about Gallagher's case.

Gallagher was acquitted in his court martial of war crimes charges that included shooting civilians, murdering a captured ISIS fighter. He was convicted of the lesser charge of posing with the corpse.

During the conversation, Esper learned that Spencer had previously and privately proposed to the White House - contrary to Spencer's public position - to restore Gallagher's rank and allow him to retire with his Trident pin, the special warfare insignia.

Trump supported the decision of his Defence Secretary.

"I was not pleased with the way that Navy Seal Eddie Gallagher's trial was handled by the Navy. He was treated very badly but, despite this, was completely exonerated on all major charges. I then restored Eddie's rank," he said in a tweet.

"Likewise, large cost overruns from past administration's contracting procedures were not addressed to my satisfaction. Therefore, Secretary of the Navy Richard Spencer's services have been terminated by Secretary of Defence Mark Esper," Trump tweeted.

"I thank Richard for his service and commitment. Eddie will retire peacefully with all of the honors that he has earned, including his Trident Pin," he said.

Trump announced that he will nominate US Ambassador to Norway Kenneth Braithwaite to replace Spencer.

"Admiral and now Ambassador to Norway Ken Braithwaite will be nominated by me to be the new Secretary of the Navy. A man of great achievement and success, I know Ken will do an outstanding job! Trump said.

According to CNN, Spencer was proposing a review with a secret guarantee that Gallagher would be allowed to keep his status as a Navy SEAL.

In his resignation letter to President Trump, Spencer wrote: "The rule of law is what sets us apart from our adversaries. Good order and discipline is what has enabled our victory against foreign tyranny time and again."

"Unfortunately it has become apparent that in this respect, I no longer share the same understanding with the Commander in Chief who appointed me, in regards to the key principle of good order and discipline," he said.

"I cannot in good conscience obey an order that I believe violates the sacred oath I took," he added.

Spencer was not fired for failing to carry out Trump's wishes.....but he was fired for going around his own chain of command -- namely Defence Secretary -- and straight to the White House, a violation of military policy, CNN reported.

Meanwhile, Gallagher issued a statement on Sunday, thanking his family, legal team and supporters that ended by heaping praise on Trump.

"President Donald Trump you have my deepest gratitude and thanks. You stepped in numerous times and showed true moral fibre by correcting all the wrongs that were being done to me. You are a true leader and exactly what the military and this nation needs," Gallagher said.

Senate Minority Leader Chuck Schumer, in a statement said he had spoken with Spencer and offered support.

"Secretary Spencer did the right thing and he should be proud of standing up to President Trump when he was wrong, something too many in this administration and the Republican Party are scared to do," the Democratic Party lawmaker said.

"Good order, discipline, and morale among the Armed Services must transcend politics, and Secretary Spencer's commitment to these principles will not be forgotten," he added.