Syrian government warplanes pounded an Islamic State group stronghold as well as other towns controlled by the rebels, conducting a wave of airstrikes Sunday that killed at least 11 people, activists said.

For more than a year, President Bashar Assad’s air force rarely targeted territory controlled by the Islamic State group in northern Syria, instead focusing on mainstream rebel groups. But government jets have begun hitting the rebels more regularly since they overran much of neighboring northern and western Iraq in June.

Even in that context, the intensity of Sunday’s air raids appeared unusually high, with at least 25 strikes hitting the group’s stronghold of Raqqa in northeastern Syria, the Britain-based Syrian Observatory for Human Rights said.

Observatory director Rami Abdurrahman said 14 of those raids targeted a military court and other buildings used by the group.

He said at least 31 Islamic State members were killed in Raqqa, and around 40 wounded. He said there were an additional 22 civilian casualties, but he didn’t have an exact breakdown of the dead and wounded.

The Local Coordination Committees, an activist collective, also reported the airstrikes on Raqqa, but put the death toll early in the day at 11.

Differences in casualty figures are common in the immediate aftermath of attacks in Syria.

Both activist groups also reported government airstrikes on Islamic State-controlled areas in Deir el-Zour province bordering Iraq and Aleppo province bordering Turkey, including the towns of Akhtarin and Dabiq.

Both communities were among around a dozen towns and villages that fighters from the extremist group overran last week in Aleppo province. Those gains have jeopardized the mainstream rebels’ position in the province as well as the city of Aleppo itself, where opposition fighters are also under assault by government troops.

They have also brought the rebel group, whose fighters have been bolstered by U.S. heavy weapons looted from Iraqi military bases, closer to a confrontation with Syrian government forces in Aleppo. The desire to weaken the group may be one reason for the uptick in airstrikes on it.

The government may also be trying to dispel long-held questions about its determination to directly confront the group, while also countering calls by rebels for the United States to conduct airstrikes against the rebels in Syria.

The main Western-backed opposition group called Saturday for U.S. warplanes to target the Islamic State group in Syria to help the mainstream rebels, whose control over half of Aleppo city, a key battleground in the civil war, is looking increasingly precarious.

The Coalition has long appealed for more robust military support from the West to help in its fight to oust Assad, and more recently to counter the rise of Islamic radicals.

The group’s latest appeal appeared aimed at capitalizing on the recent U.S. aerial intervention in neighboring Iraq, where American military aircraft have targeted the Islamic State group.

But President Barack Obama has long refused demands for similar action in Syria, fearing it could draw the U.S. into an increasingly complex and bloody civil war. SAPA