The legislation notes that about 28,500 American troops are currently stationed in South Korea as a demonstration of the US commitment to the bilateral alliance.

Their "significant removal" is "a non-negotiable item as it relates to the complete, verifiable, and irreversible denuclearization" of North Korea, it says under a section describing the Sense of Senate on US military forces on the Korean Peninsula.

In a conference report accompanying the legislation, Congress also prohibits the use of the funds to reduce the troops' number below 22,000 without certification from the secretary of defense that "such a reduction is in the national security interest of the United States and will not significantly undermine the security of United States allies in the region."

The defense secretary would also be required to certify that he has "appropriately consulted with allies of the United States, including the Republic of Korea (South Korea) and Japan, regarding such a reduction."

The restriction comes as Trump has repeatedly indicated a willingness to eventually pull out American forces from South Korea. Critics say such a move would play into the hands of China and North Korea, which wish to see US troops removed from near their border. (Yonhap)