American jets began bombing ISIS targets in Syria early Tuesday, raising U.S. involvement in the war-torn country and sending a forceful message to the terror group.

The airstrikes focused on the ISIS stronghold of Raqqa, a U.S. official told CNN, though other locations were hit as well. They're the first strikes against the terror group inside the country since President Barack Obama's announcement this month that he was prepared to expand the American efforts beyond targets in Iraq.

All foreign partners participating in the strikes with the United States are Arab countries, a senior U.S. military official told CNN. Those nations are Bahrain, Saudi Arabia, the United Arab Emirates and Jordan.

Diplomatic sources told CNN that Qatar was also involved, though it was not clear whether Qatar actually conducted airstrikes itself.

The U.S. and "partner nation forces" began striking ISIS targets using fighters, bombers and Tomahawk missiles, Pentagon spokesman Rear Adm. John Kirby said, though he didn't specify a geographic location.

Citing the ongoing operations, Kirby said the Pentagon would not provide additional details immediately. But a U.S. military official said the strikes are meant to target the ability of ISIS to command and control, resupply and train.

Tomahawk missiles launched from the sea initiated the strike, followed by bombers and fighters, a senior U.S. military official told CNN.

The goal with this first move is to have an initial, definitive blow, the official said, describing the pace of the operation as intense.

Most of the spots hit were hard targets such as buildings, a senior U.S. official told CNN.

A post office, a recruitment center and a building in the governor's compound were among the structures in Raqqa hit by U.S. airstrikes, Syrian opposition activists said.

There was no immediate word about casualties, the activists said.

Power went out in the city shortly after the airstrikes but was restored later Tuesday morning.

(CNN)