(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.

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

Military analyst: Strikes are 'symbolic'

But 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."

What impact did airstrikes have?

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.

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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.