US defence chief Mattis says Trump is '100 percent' with him

His remark comes after US broadcaster CBS on Sunday aired an interview with Trump, in which he suggested Mattis may be headed out the Pentagon door.

US defence chief Mattis says Trump is '100 percent' with him

US Defense Secretary Jim Mattis said President Donald Trump has assured him of his full support, one day after Trump appeared to cast doubt over the Pentagon chief's fate.

Speaking to reporters as he flew from Washington to Ho Chi Minh City at the start of a diplomatic tour that will take him to Vietnam and Singapore, Mattis said he had spoken directly to Trump by phone late Monday morning Washington time.

"He said, 'I'm 100 percent with you'," Mattis said.

"It could be that he is. I think he's sort of a Democrat, if you want to know the truth," Trump said.

"But General Mattis is a good guy. We get along very well. He may leave. I mean, at some point, everybody leaves."

Earlier on in the 20-hour flight to Vietnam -- before he'd spoken to Trump, who himself was flying on Air Force One to Florida -- Mattis was asked what he'd made of Trump's comments. 

"Nothing at all," Mattis said.

"I'm on his team. We have never talked about me leaving. And as you can see right here, we are on our way, we just continue doing our job... no problem."

He added that he had never registered with any political party, and that those in the military are "proudly apolitical".