FILE - U.S. military advisers from the 1st Security Force Assistance Brigade sit at an Afghan National Army base in Maidan Wardak province, Afghanistan, Aug. 6, 2018.
FILE - U.S. military advisers from the 1st Security Force Assistance Brigade sit at an Afghan National Army base in Maidan Wardak province, Afghanistan, Aug. 6, 2018.

U.S. Defense Secretary James Mattis on Tuesday rebuffed a proposal to withdraw American troops from Afghanistan and replace them with private security forces.

"When the Americans put their nation's credibility on the line, privatizing it is probably not a wise idea," Mattis told reporters.