President Joe Biden's State Department and Pentagon on Thursday promised a smooth transition to the team of Donald Trump, who has promised major shake-ups.
US Secretary of State Antony Blinken expects to have "appropriate engagement" with his designated successor, Senator Marco Rubio, "in the weeks and time ahead," State Department spokesman Vedant Patel told reporters.
"We of course congratulate Senator Rubio on this announcement," Patel said.
Rubio is known for his hawkish views on China, Iran and Latin American leftists, but is largely seen as within the mainstream of US foreign policy.
Trump picked a far less-known figure to head the Pentagon -- Fox News host and National Guard veteran Pete Hegseth.
Rubio is virtually assured Senate confirmation but Hegseth could face tough questions about his competency -- though Trump's Republican Party will control the chamber and the president-elect has spoken of bypassing a vote through a controversial procedural move.
"We are going to do everything that we can to ensure that there is an orderly, calm transition, and so when the incoming secretary's team is ready to make that transition, we want to ensure that they are set up for success," Pentagon spokeswoman Sabrina Singh told reporters.
Hegseth, 44, who has never held a major management position, would be in charge of a sprawling institution of 3.4 million troops and civilians and an annual budget of $850 billion.
Trump and Hegseth have in the past called for the removal of some uniformed officers, in part due to perceived disloyalty to the president-elect.
Asked if the next administration could sack uniformed officers, Singh did not respond directly but noted that a Trump ally, Senator Tommy Tuberville, held up the nominations of 425 officers for months in a dispute over abortion policy.
The Senate finally pushed through the confirmations at the end of 2023.
"You remember the time when we had a significant amount of holds on our general and flag officers," Singh said.
The holds on new nominations and promotions forced others to do multiple jobs and had "an impact to operations."
"That's going to have an impact to morale, and that is going to have an impact on the department," she said.
Biden on Wednesday met in the Oval Office with Trump, reviving a tradition that Trump had jettisoned in 2020.
Trump denied Biden's victory, skipped his inauguration and spoke to a rally that turned into a deadly assault on the US Capitol as lawmakers certified Biden's win.