Marines from an amphibious task force have left their ships in the Middle East and deployed to Syria, establishing an outpost from which they can fire artillery guns in support of the fight to take back the city of Raqqa from the Islamic State, defense officials said.

The deployment marks a new escalation in the U.S. war in Syria, and puts more conventional U.S. troops in the battle. Several hundred Special Operations troops have advised local forces there for months, but the Pentagon has mostly shied away from using conventional forces in Syria. The new mission comes as the Trump administration weighs a plan to take back Raqqa, the so-called capital of the Islamic State, that also includes more Special Operations troops and attack helicopters.

The force is part of the 11th Marine Expeditionary Unit, which left San Diego on Navy ships in October. The Marines on the ground include part of an artillery battery that can fire powerful 155-millimeter shells from M777 Howitzers, two officials said, speaking on the condition of anonymity because of the sensitivity of the deployment.