France launched “massive” air strikes on the Islamic State group’s headquarters in Syria on Sunday night, leveling a jihadi training camp in Raqqa, where Iraqi intelligence officials say the attacks on Paris were planned.

Twelve aircraft — including 10 fighter jets, launched from sites in Jordan and the Persian Gulf — dropped 20 bombs in the biggest air strikes since France extended its bombing campaign against the extremist group to Syria in September.

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French police, meanwhile, announced seven arrests and hunted for more members of the sleeper cell that carried out the Paris attacks that killed 129 people.

At least one man with connections to the Paris attacks had registered as a refugee with Greek authorities earlier this year, officials said. A Syrian passport was found near the body of a dead suicide bomber.

“We confirm that the (Syrian) passport holder came through the Greek island of Leros on October 3 where he was registered under EU rules,” the Greek minister for citizen protection said in a statement.