The Pentagon chief made it clear Saturday that his country is not negotiating with North Korea on the future of American troops stationed on the peninsula, as the leaders of the two sides will soon meet here each other.
Speaking at a security forum, Secretary of Defense Jim Mattis stressed that the fate of the 28,500-strong U.S. Forces Korea is not an issue to discuss with North Korea.
"That issue is not on the table here in Singapore on the 12th (of June), nor should it be," he said after a speech at a Shangri-La Dialogue session.
Hours earlier, President Donald Trump met with Kim Yong-chol, a top North Korean official, at the White House. Following the meeting, Trump said he plans to meet with the North's leader Kim Jong-un in Singapore on June 12.
The White House meeting is a highlight of a series of pre-summit consultations between the two sides taking place at Panmunjom on the inter-Korean border, in the U.S. and in Singapore.
The North has long claimed that the U.S. military presence in Korea is the major roadblock to regional peace and the reunification of the two Koreas.
Mattis said the issue of scaling down the U.S. military presence in Korea or withdrawing the troops is "subject to discussions" between the allies, separate from negotiations with North Korea.
He said Seoul and Washington could talk about the matter in the future in case of significant progress in efforts to reduce regional security challenges, apparently referring to the North's nuclear weapons and missile program.
"Obviously, if diplomats can do their work, if we can reduce the threat, if we can restore confidence-building measures with something verifiable, then of course this type of issue can come up subsequently between the two sovereign democracies -- the Republic of Korea and the United States," he said.