WASHINGTON • United States President Donald Trump has hinted that Defence Secretary James Mattis might be planning to quit his administration, and described the former US Marine Corps general as "sort of a Democrat".

In an excerpt from a 60 Minutes interview that aired on Sunday on CBS, Mr Trump talked about the level of turnover in his administration after almost two years, and suggested that there could be more to come. "There are some people that I'm not happy with. I have some people that I'm not thrilled with. And I have other people that I'm beyond thrilled with," he said, according to a transcript provided by CBS.

Mr Mattis "hasn't told me" that he plans to leave, Mr Trump said, and did not directly answer the question whether he would like the Pentagon chief to depart.

"I had lunch with him two days ago. I have a very good relationship with him. It could be that he is. I think he's sort of a Democrat, if you want to know the truth," the Republican President said. "He may leave. I mean, at some point, everybody leaves. Everybody. People leave. That's Washington."

Mr Mattis was one of Mr Trump's first Cabinet picks after the 2016 election. He was long seen as a force for stability in foreign policy in an administration that has had to manage crises from North Korea to Syria under a President who prides himself on his unpredictability.

But the Pentagon chief has been on the defensive after excerpts from author Bob Woodward's book Fear painted the publicly taciturn military man as being critical of Mr Trump in private.

Mr Trump's comments come ahead of a visit to Vietnam and Singapore this week by Mr Mattis.

He departed yesterday for Vietnam and will attend the Asean Defence Ministers' Meeting in Singapore.

BLOOMBERG