The Pentagon will send another 200 Special Operations troops to Syria, a senior official said on Saturday, substantially expanding the U.S. military footprint as part of an effort to topple the Islamic State capital there.

Defense Secretary Ashton B. Carter, speaking at a conference in Bahrain, said the troops would include trainers, advisers and explosives specialists.

He said the increase would better enable the United States to support allied Syrian forces who were now only 15 miles from Raqqa, the central Syrian city where the Islamic State is expected to make its final stand.

The Obama administration currently has about 300 Special Operations troops in Syria. American ground troops are “bringing down to bear the full weight of U.S. forces around the theater of operations like the funnel of a giant tornado,” according to prepared remarks released before his address.

A senior defense official said the new forces were “tied to the growing number of local forces now willing to participate in this fight, and our efforts to enable them.”

The announcement comes as U.S. military commanders seek to advance plans, which President Obama approved in October, to launch an operation to capture Raqqa using a Kurdish-dominated group known as the Syrian Democratic Forces.

Military leaders hoped the operation will increase pressure on the Islamic State amid the ongoing offensive to take Mosul, the Iraqi city also home to a significant militant presence. But they have faced major challenges, including the difficulty of finding enough Arab fighters.

A military offensive by Turkey, which views the U.S.-backed Kurdish forces as part of a insurgent group threatening its own core interests within Syria, has only complicated that difficult mission.