U.S. Defense Secretary Jim Mattis said the diplomatic push to solve the North Korean nuclear weapons crisis was at such a delicate stage that he won't publicly discuss the talks or related issues such as U.S.-South Korean military exercises.

Mattis was among advisers who were in the White House when President Donald Trump on Thursday decided to accept the offer by North Korean leader Jong Un Kim to meet by May. The offer was relayed to Trump by a South Korean government delegation that briefed the president on their meeting with Kim last week in the North Korean's capital.

"I do not want to talk about Korea at all. It's that delicate,'' he said in an interview as he flew to the Mideast, landing in Oman on Sunday.

"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 U.S.-South Korean military maneuvers 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.

Trump said 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 honor that commitment,'' the president said.

Later, at a political rally in Pennsylvania, when Trump mentioned Kim's name, the crowd booed but 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." (AP)