The United States and several Arab nations carried out airstrikes against ISIS in Syria early Tuesday, intensifying the campaign against the Islamic militant group. Tomahawk missiles launched from the sea began the strikes against the Sunni Muslim extremists, followed by bombers and fighters. Here are answers to key questions about the new phase in the conflict with ISIS: Which areas were hit? The bombing has focused on the ISIS stronghold of Raqqa, a city in northern Syria. ISIS has had control of Raqqa for more than a year, imposing its brutal interpretation of Islamic law on the city's residents.
@highlight
The strikes focus on Raqqa, the de facto capital of ISIS' self-declared Islamic state
@highlight
Saudi Arabia, Jordan, the UAE, Qatar and Bahrain take part, the U.S. military says
@highlight
"It's a remarkable diplomatic achievement," says a CNN political commentator
@highlight
Pentagon: The sites hit include training compounds, headquarters, storage facilities
The militant group has increased security patrols in @placeholder, an opposition activist told CNN.