President Donald Trump says drawing down US troops in South Korea is not on the table for his upcoming talks with North Korea's Kim Jong Un, which will be focused on pressing the Asian nation to abandon nuclear weapons.

Trump made the comments at a White House event on trade negotiations with China on Friday.

Senior Trump administration officials said on Thursday the two sides will not discuss removing US troops from South Korea and will focus on seeking a common understanding of what it means to denuclearise when they meet in Vietnam at the end of the month.

The United States keeps some 28,500 troops in South Korea.