President-elect Donald Trump plans to nominate retired Marine General John Kelly to lead the Department of Homeland Security, CBS News reported on Wednesday.

Kelly, the former head of the U.S. Southern Command, has accepted the offer, CBS said, citing unidentified sources.

Reuters has not independently confirmed the choice.

Kelly, 66, would be the third general Trump has tapped for a high-level position in his administration.

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Security supremo: John Kelly, the retired Marine Corps general who is being nominated for Homeland Security. He met with the president-elect on November 30 and is being named by sources as Trump's pick

General in charge: Retired Marine General James 'Mad Dog' Mattis flew with Donald Trump to North Carolina on Tuesday to be officially unveiled as his choice for the Pentagon

General at his side: Michael Flynn, a retired Army lieutenant general, is Trump's choice for national security adviser

The Republican president-elect, who has no military experience, planned to nominate retired General James Mattis to lead the Department of Defense and picked retired Lieutenant General Michael Flynn to be his national security adviser.

Kelly differed with Democratic President Barack Obama on key issues and has warned of vulnerabilities along the United States' southern border with Mexico.

As head of the U.S. Southern Command, his final leadership post in a 45-year military career, Kelly was responsible for U.S. military activities and relationships in Latin America and the Caribbean.

Kelly is also the highest ranking military officer to have lost a child in combat

1st Lieutenant Robert Michael Kelly, John Kelly’s son, was killed on November 9, 2010 in Afghanistan at the age of 29.

'He went quickly and thank God he did not suffer', John Kelly said of his son's landmine death in Sangin Afghanistan in 2010

He was leading a platoon of Marines in Sangin, where he took part in some of the most intense fighting of the war, killing dozens of Taliban fighters.

He died instantly when he stepped on a land mine.

'He went quickly and thank God he did not suffer', John Kelly said of his son's death, according to the Los Angeles Times.

'In combat that is as good as it gets'.

Although Kelly's military experience may give him insight into overseas threats, like drug trafficking or Islamic extremism, it will do little to prepare him for the legal and political complexities of grappling with a sprawling agency that oversees everything from airport security to protecting against cyber threats and responding to domestic crises.

Trump's most senior appointment is that of 'Mad Dog' Mattis to the Pentagon.

At a rally in North Carolina on Tuesday evening, Trump introduced him to the crowd and said he would be 'incredible'.

He also warned Congress that if it doesn't give a special waiver to Mattis, people will be 'angry.' Democrats are balking at the procedure Republicans are trying to use to fast-track the waiver.

Trump brought Mattis before a cheering crowd in Fayetteville, a military town that is home to Fort Bragg and other installations.

'He'll get that waiver, right?' Trump told the crowd.

'Oh, if he don't get that waiver there'd be a lot of angry people,' Trump warned.

'Such a popular choice,' he observed.

Approval: Trump met Kelly at his golf club in Bedminster, New Jersey, on 20 November and again at Trump Tower 10 days later for talks

'What a great guy he's gonna be incredible,' Trump said. 'Mad Dog plays no games, right?' Trump observed, using Mattis' nickname.

Democrats are complaining about a GOP leadership move to expedite a waiver for Donald Trump's pick to lead the Pentagon, retired Gen. James Mattis

Congress must provide a waiver to Mattis to overcome a 1947 statute on civilian control of the military that states that the Defense head must have been out of uniform for at least seven years.

Mattis has 'committed his life to his love for our country,' Trump said. 'General Mattis is the living embodiment of the Marine Corps motto: semper fidelis – always faithful,' Trump said.

He said Mattis 'will now be the civilian leader atop the Department of Defense.'

Mattis, wearing a dark suit, made brief remarks that acknowledged the sensitivity of the situation.