Syrian government airstrikes, including one on a crowded sheep market, killed at least 11 people on Thursday in a northern town controlled by the Islamic State group, activists said.

But the government has long deployed its heaviest air power against mainstream and Islamist rebel groups, and on Thursday it launched 12 airstrikes on the town of Douma, east of Damascus, that smashed buildings and killed at least nine people, activists said. The area is mainly controlled by rebel groups, and Islamic State militants have little if any presence there.

After largely ignoring the rise of the al-Qaida splinter group over the past year, President Bashar Assad’s air force has begun to target Islamic State militants more regularly since the extremist faction seized control of much of northern Syria and a large part of neighboring Iraq in June. […]