US defence secretary Jim Mattis has said the diplomatic push to solve the North Korean nuclear weapons crisis was at such a delicate stage that he will not publicly discuss the talks.
Mr Mattis was among advisers who were at the White House when President Donald Trump on Thursday decided to accept the offer from North Korean leader Kim Jong Un to meet by May.
The offer was relayed to Mr Trump by a South Korean government delegation that briefed the president on their meeting with Kim last week in the North Korean capital.
"I do not want to talk about Korea at all. It's that delicate," Mr Mattis said as he flew to the Middle East.
"When you get in a position like this, the potential for misunderstanding remains very high," he said, explaining his unwillingness to talk about any aspect of the diplomatic efforts.
The Pentagon chief said the White House and State Department were best suited to discuss the situation in advance of the May meeting.
He declined to discuss the timing and scale of annual US-South Korean military manoeuvres that were postponed during the recent Winter Olympics in South Korea. Those exercises are expected to be held in April, but no official announcement has been made.
Mr Trump said on Saturday he believes North Korea will abide by its pledge to suspend missile tests while he prepares for the summit. He noted in a tweet that North Korea has refrained from such tests since November and said Kim "has promised not to do so through our meetings."
"I believe they will honour that commitment," the president said.
Later, at a political rally in Pennsylvania, when Mr Trump mentioned Kim's name, the crowd booed but Mr Trump responded: "No, it's very positive... no, after the meeting you may do that, but now we have to be very nice because let's see what happens, let's see what happens."
- Press Association