PARIS — (CNN) French fighter jets bombed a series of ISIS sites in Raqqa, Syria, on Sunday in what officials described as a major bombardment.

The airstrikes came two days after a series of terrorist attacks in Paris. ISIS has claimed responsibility for the attacks, which France’s President described as “an act of war.”

ISIS claims Raqqa as the capital of its so-called caliphate. The targets in Sunday’s airstrikes included a command center, a recruitment center, an ammunition storage base and a training camp for the terror group, said Mickael Soria, press adviser for France’s defense minister.

Twelve aircraft, including 10 fighter jets, were involved in the airstrikes, Soria said. Twenty bombs were dropped, he said, and all of the targets were destroyed.

An ISIS media wing claimed the sites had been abandoned before they were hit and said there were no casualties.

France has been conducting airstrikes against ISIS targets in Syria since September as part of a U.S.-led coalition.

A senior Obama administration official said that the United States was “working closely with the French to develop targets.”

The U.S. military likely handed over a list of targets the coalition was planning to strike to the French to let them fly the sorties, said Ret. Lt. Gen. Mark Hertling, a military analyst. “These target packages were already in folders, as they’re called, and I’m sure the central command handed them over to the French fighters to attack for the symbolism of France being back in the fight.”

The timing of Sunday’s airstrikes likely was no coincidence, analysts said.

“Clearly, it’s a military activity, but it really sends a very strong political message, and it’s all for internal consumption within France,” said retired Maj. Gen. James “Spider” Marks, a CNN military analyst.

“This is very visceral. The types of targets they strike right now really are symbolic. From the French perspective, something has to be done.”

But it’s difficult to know what’s going on inside the ISIS stronghold, said Janine di Giovanni, Newsweek’s Middle East editor. And it’s also hard, she said, to gauge the best strategy for fighting back.

“I think that it’s very complicated, launching airstrikes like this as a retribution, but also as a way of wiping out ISIS,” she said. “Because, the other thing is, that you can’t wipe out an ideology. You might be able to suppress them militarily, or you might be able to cut off some of their lines, but you can’t suppress the key message they’re spreading.”

The planes involved in the French airstrikes took off from the United Arab Emirates and Jordan in a mission carried out in coordination with U.S. forces, the French defense ministry said in a statement late Sunday.

The sites targeted inside Raqqa were identified in previous French reconnaissance missions, the statement said.

But what impact did the airstrikes have?

It’s hard to know what’s happening on the ground inside Raqqa. Since ISIS took over, the city has become increasingly isolated — with an activist group known as Raqqa is Being Slaughtered Silently providing outsiders with a harrowing glimpse of the city’s transformation.

On Sunday, the activist collective said that the city appeared to be bracing for an attack even before the French airstrikes began.

ISIS fighters in Raqqa had expected retaliatory airstrikes and evacuated key facilities, including their headquarters, operation and security buildings, a member of Raqqa is Being Slaughtered Silently said.

Streets were empty, the activists said, markets were less crowded than usual and sheikhs in mosques said they expected the city to be struck.

The airstrikes hit several key ISIS facilities, including the city’s stadium, activists said, used by ISIS as both its headquarters and a jail. It was not immediately clear what the damage was. So far, according to Raqqa is Being Slaughtered Silently, there have been no reports of civilian casualties.

The ISIS media wing Amaaq also said the sites hit by airstrikes had been abandoned and that no one had been killed in the airstrikes. CNN has not independently confirmed the groups’ reports.

ISIS in Raqqa was previously the target of retaliatory airstrikes in February. Two days after news emerged that the group had burned a captive Jordanian pilot to death, the Middle Eastern nation hit back.

At the time, ISIS posted photos of the destruction from the Jordanian airstrikes and the activist Syrian Observatory for Human Rights said 10 militants were killed.

The-CNN-Wire ™ & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: French Defense Ministry/CNN)