Programming Note: Former Vice President Dick Cheney sits down with Sean Hannity to give his take on the latest military action in Syria. Don't miss a "Hannity" exclusive, Wednesday at 10p ET.

Twelve days after President Obama announced the launch of a major military operation against the ISIS terror group, the U.S. and allies have begun airstrikes in Syria.

The U.S., along with a coalition of five Arab countries - the United Arab Emirates, Saudi Arabia, Jordan, Bahrain and Qatar - began bombing the ISIS stronghold city of Raqqa ​with multiple aircraft, including bombers, fighters and drones, striking at about 20 to 25 ISIS targets, reportedly including command and control centers, training camps and weapons depots, according to officials.

WATCH: Amateur Video Claims to Show U.S. Airstrikes Against ISIS in Syria

Gen. Keane: ISIS Didn't Believe U.S. Would Strike in Syria reported:

Sources say the military operation includes fighter jets, B-1 bombers and Predator drones, as well as Tomahawk missiles launched from the Red Sea and Persian Gulf.

Officials say the coalition is targeting about 20 sites, including command-and-control centers, training camps and weapons depots.

U.S. officials told Fox News that several Arab countries – including Saudi Arabia, Jordan, Bahrain and the United Arab Emirates – were participating.

The operation was expected to last several hours, with the first explosions from Tomahawk missiles heard near Raqqa, the Islamic State stronghold in northern Syria

U.S. aircraft include B-1 bombers, F-16s, F-18s and Predator drones, with F-18s flying missions off the USS George H.W. Bush in the Persian Gulf. Tomahawk missiles were fired from the destroyer USS Arleigh Burke in the Red Sea.

The military strikes come less than two weeks after President Obama, on Sept. 10, authorized U.S. airstrikes inside Syria as part of a broad campaign to root out the Islamic State militant group, also known as ISIS or ISIL.

In a nod to his plans to go into Syria, Obama said then, “I have made it clear that we will hunt down terrorists who threaten our country, wherever they are. That means I will not hesitate to take action against ISIL in Syria, as well as Iraq.”

Until now, U.S. airstrikes have been limited to specific missions in northern Iraq. Lawmakers and military advisers, though, had stressed for weeks that any campaign against the Islamic State would have to include action in Syria, where the militant network is based.

Because the United States had stayed out of the Syria conflict for so long, the Obama administration had spent the last several weeks scrambling to gather intelligence about possible targets in Syria, launching surveillance missions over the country last month.

Pentagon Press Secretary Rear Adm. John Kirby released a statement Monday night saying, "I can confirm that U.S. military and partner nation forces are undertaking military action against ISIL terrorists in Syria using a mix of fighter, bomber and Tomahawk Land Attack Missiles.

"Given that these operations are ongoing, we are not in a position to provide additional details at this time. The decision to conduct theses strikes was made earlier today by the U.S. Central Command commander under authorization granted him by the commander-in-chief."

Watch Megyn Kelly speak to Jennifer Griffin about the airstrikes in the clip from "The Kelly File" above, hear Rep. Peter King (R-NY) react below and stay with Fox News Insider for updates.

O'Reilly: Does President Obama Have the Guts to Raise an 'Anti-Terror Force' to Fight ISIS?

Watters’ World: How Would College Students Deal With ISIS?