"This is a diplomatically led effort," Mattis told reporters when asked about a possible meeting between President Donald Trump and North Korean leader Kim Jong Un.

"When you get into a position like this, the potential for misunderstanding remains very high... so I want those who are actually engaging in the discussions to be the ones who answer all media questions about it," he added.

"Right now, every word is going to be nuanced and parsed apart across different cultures at different times of the day in different contexts, and right now I want a very straight line from those actually responsible, not from those of us in a supporting or background role," Mattis said.

Top South Korean official Chung Eui-yong announced Thursday that Kim and Trump will meet by May to secure a deal to remove nuclear weapons from the Korean peninsula.

Mattis was among the senior officials present in the White House when Trump accepted the invitation.

Chung said Kim is committed to denuclearisation, and Kim had pledged that North Korea would refrain from any further nuclear or missile tests during talks.

Mattis did not comment when asked about Foal Eagle joint drills with South Korea, which are expected to begin in the coming weeks.