The president noted gains made by the current 50 special operators in missions to advise and assist local forces batting the Islamic State, which holds territory in Syria and Iraq.

“Given the success, I’ve approved the deployment of up to 250 additional U.S. personnel . . . to keep up this momentum,” Obama said in a speech that also focused broadly on European issues.

Obama emphasized that the new troops are “not going to be leading the fight on the ground” but that they would work with local forces.

The expanded U.S. military presence in Syria is aimed in part at helping to expand the ranks of Arab fighters in a network of groups, now dominated by Kurdish fighters, that the United States is backing as it battles the Islamic State. The additional U.S. forces work with Kurdish militiamen and others as they seek to isolate Raqqa, the Islamic State’s de facto capital in Syria.