Beirut: At least 31 Islamic State of Iraq and the Levant (Isil) militants were killed in Syrian air force raids on Sunday in the northern province of Raqqa, a stronghold of the militants, a monitoring group said.

“The regime carried out 13 raids on the city of Raqqa and 11 on the town of Tabqa in Raqqa province, killing at least 31 militants and wounding dozens of them,” said the Syrian Observatory for Human Rights.

The Britain-based group’s head, Rami Abdul Rahman, said the raids were the regime’s “most intensive” against the Isil since the militants joined the more than three-year-old conflict in Syria in spring 2003.

Isil has held most of Raqqa province since February, after having ousted other rebel groups battling President Bashar Al Assad’s regime.

The Observatory said the regime has also carried out air strikes on the eastern province of Deir Al Zor as well as Akhtarin and Dabeq in Aleppo province, two northern towns which Isil seized from rebels on Wednesday.

The Syrian military has turned its firepower on Isil since the militants in June declared a “caliphate” straddling Syria and neighbouring Iraq, where the group has been targeted by US air strikes over the past week.

“The regime wants to show the Americans that it is also capable of striking Isil,” said Abdul Rahman, whose group relies on information from opposition activists and medics on the ground.

“The regime strikes Isil where it is strong. In regions where the group is confronted by rebels, it doesn’t intervene so that the two enemies weaken each other,” he said.

“But once one party takes the upper hand, it strikes,” said Abdul Rahman.

Since joining Syria’s conflict, Isil has also seized most of Deir Al Zor, another province on the Iraqi border, spreading terror as it imposes its own strict interpretation of Islam with penalties such as beheadings.