WASHINGTON—The Trump administration is weighing a withdrawal of thousands of American troops from South Korea, according to military officials familiar with the discussions, a move that could stir new anxiety among allies worried about the White House commitment to Asia.

South Korea's defence ministry said on Friday that Seoul and Washington had not had discussions about the withdrawal of some U.S. troops stationed in the country. The ministry made the comment in response to a report by the Wall Street Journal that said the U.