The issue of U.S. troops stationed in South Korea will not be "on the table" at a summit this month between President Donald Trump and North Korea's Kim Jong Un, U.S. Defense Secretary Jim Mattis said Saturday.

"That issue is not on the table here in Singapore on the 12th (of June), nor should it be," he said at the Shangri-La Dialogue, a security summit in Singapore, referring to the scheduled date of the Trump-Kim meeting.

There are currently some 28,500 U.S. forces based in the South.