The former chairman of the Joint Chiefs of Staff under Presidents George W. Bush and Obama expressed concerns about the role of military officials in the Trump administration during an interview on Sunday.

Retired Adm. Mike Mullen told CNN's Fareed Zakaria that he is "extremely concerned" about generals such as White House chief of staff John Kelly John Francis KellyMORE holding political roles in President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE's White House due to their lack of political experience.

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"Jim Mattis, and John Kelly and H.R. McMaster are not politicians, but they're operating in this political world inside the White House," Mullen said. "It is a tough, difficult, political environment."

"To see John Kelly, and I'll be very specific, politicize, you know, the death of his son to support the political outcome for the president was very, very distressing to me, but speaks to the power of that environment and, quite frankly, to the lack of understanding that any of us in the military have about that environment until we get in it and have to operate in it," he said.

Mullen's comments come as speculation swirls around the future of Kelly's role in the White House.

Axios reported on Saturday that Kelly threatened to quit last month after Trump decided to fire former Veterans Affairs Secretary David Shulkin David Jonathon ShulkinVA inspector general says former top official steered M contract to friend Schumer demands answers in use of unproven coronavirus drug on veterans Former Trump VA secretary says staffer found plans to replace him in department copier MORE, while The Washington Post published a story suggesting that Kelly was losing his power in the White House.

Trump hit back at the speculation in a tweet on Sunday.