The U.S. will withdraw about 600 troops from Syria, leaving fewer than 1,000 to work with Kurdish allies to counter the Islamic State group, a U.S. official said. The U.S. troops have been critical not only in the operations against the Islamic State but as a buffer for the Kurdish forces against Turkey. The departure of the 600 troops will return force levels to where they had been for years, after the U.S. and its allies waged a multiyear campaign to defeat IS.