The Trump administration plans to expand the number of U.S. diplomats and contractors in eastern Syria to help stabilize the once Islamic State-controlled part of the country, Defense Secretary Jim Mattis said Friday.

Mr. Mattis didn’t provide any details about how many U.S. personnel would be sent or when, but he cited two Syrian cities that would receive U.S. help—Tabqa and Raqqa, the de facto Islamic State capital until it fell out of its control this year.

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