Retired Vice Admiral Robert Harward has turned down an offer to be US President Donald Trump's new national security adviser, the latest blow to a new administration struggling to find its footing.

Key points: National security advisor Michael Flynn was fired after just 24 days in office due to his ties with Russia

National security advisor Michael Flynn was fired after just 24 days in office due to his ties with Russia Robert Harward was chosen to replace Mr Flynn, but declined due to family and financial reasons

Robert Harward was chosen to replace Mr Flynn, but declined due to family and financial reasons Admiral Harward reportedly wanted to bring in his own team

Admiral Harward was offered the job after Michael Flynn was fired by Mr Trump earlier this week for misleading Vice-President Mike Pence over his conversations with Russia's ambassador to the United States.

He said that the Trump administration was "very accommodating to my needs, both professionally and personally".

"It's purely a personal issue," Admiral Harward said.

"I'm in a unique position finally after being in the military for 40 years to enjoy some personal time."

Admiral Harward, a former Navy SEAL, was asked whether he had requested to bring in his own staff at the National Security Council (NSC) and replied "I think that's for the president to address".

It was earlier reported that two sources familiar with the decision had said Admiral Harward turned down the job in part because he wanted to bring in his own team.

That would have put him at odds with Mr Trump, who had told Mr Flynn's deputy, KT McFarland, that she could stay.

The President also made clear why he asked Mr Flynn to resign, saying it was because the retired Lieutenant-General had not been completely truthful with Mr Pence about his conversations with the Russian ambassador to the United States, Sergei Kislyak.

"The thing is, he didn't tell our Vice-President properly, and then he said he didn't remember," Mr Trump said.

"So either way, it wasn't very satisfactory to me."

Harward served under General Mattis

Admiral Robert Harward is now a senior executive at Lockheed Martin. ( AP: US Marine Corps )

Admiral Harward served as deputy commander of US Central Command under General James Mattis, who is now defence secretary.

He also served on the National Security Council under President George W Bush and commissioned the National Counter Terrorism Centre.

Upon retirement in 2013 after a nearly 40-year career in the Navy, Admiral Harward became chief executive officer for defence and aerospace giant Lockheed Martin in the United Arab Emirates.

Mr Trump has recently been in very public negotiations with Lockheed over the cost of its F-35 fighter jet.

Officials said earlier this week that there were two other contenders in the running for the job: acting national security adviser Keith Kellogg and retired General David Petraeus.

General Petraeus, a retired four-star general, resigned as CIA director in 2012 and pleaded guilty to one misdemeanour charge of mishandling classified information relating to documents he had provided to his biographer, with whom he was having an affair.

He was also fined $100,000 and remains on probation.

Reuters/AP