US President Barack Obama has confirmed that former deputy secretary of defence Ashton Carter will be his pick to replace Pentagon chief Chuck Hagel.

Mr Obama made the announcement at a modest ceremony in the Roosevelt Room of the White House on Friday morning in Washington, hailing Mr Carter as one of the country's foremost national security leaders.

"He is an innovator who helped create the programme that has helped dismantle weapons of mass destruction around the world and reduced the threat of terrorism; he is a reformer who has never been afraid to cancel old or inefficient weapons programmes; he knows the Department of Defence inside and out; all of which means on day one he is going to hit the ground running," said Mr Obama.

He added that Mr Carter faces a long list of challenges that include dealing with Ebola and the Islamic State in Iraq and Syria militant group, strengthening alliances like the North Atlantic Treaty Organisation, and continuing the rebalance to Asia.

Mr Carter's name emerged among the short-list of possible candidates shortly after Mr Hagel's sudden resignation last week.

To Asian observers, he is known as a strong supporter of the Navy's littoral combat ship programme, an expert at wrangling the budget and for arguing for a pre-emptive strike against North Korea in 2006 to prevent a ballistic missile test.

The 60-year-old has served under 11 different defence secretaries, including the three of Mr Obama's tenure - Mr Robert Gates, Mr Leon Panetta and Mr Chuck Hagel. He left the Pentagon last year.

"I think it's fair to say, Ash, that in your one year attempt at retirement from public service, you failed miserably," joked Mr Obama.

His 2013 departure from the Pentagon last year came amid rumours that he was upset about being overlooked for the top job once again and differences with Mr Hagel.

Nothing at the otherwise feel-good ceremony on Friday served to quell any of that talk. Mr Hagel - who was due to attend the announcement - cancelled at the last minute. And in Mr Carter's list of acknowledgements during his brief remarks, Mr Hagel's name was conspicuously absent.

Mr Carter said he accepted the nomination in part because of his "deep and abiding love" for the American troops.

He also pledged to give President Obama frank advice.

"If confirmed in this job, I pledge to you my most candid strategic advice... And to the greatest fighting force the world has ever known, to you, I pledge to keep faith with you and to serve our nation with the same unflinching dedication you demonstrate every day."

Mr Carter is expected to be able to get confirmed next year, even though he faces a Republican-controlled Senate.

The incoming head of the Senate Armed Forces committee John McCain has already voiced support for the nominee.