A man and a child walk past debris following a reported air strike by Syrian government forces on June 20, 2014, in the northern city of Aleppo. (Baraa Al-Halabi/AFP/Getty Images)

The Syrian army carried out a series of airstrikes against a town in eastern Syria that was captured by fighters from an al-Qaeda breakaway group a day earlier, killing 16 people, activists said Saturday.

The Britain-based Syrian Observatory for Human Rights said the warplanes pounded parts of Muhassan with six airstrikes, adding that the casualties included three civilians.

Fighters from the Islamic State of Iraq and Syria (ISIS) stormed Muhassan, along the Euphrates River, on Friday, raising their black flags around the town after rebels from the Western-backed Supreme Military Council defected to the jihadist group, activists said.

The town is in the eastern province of Deir el-Zour, which borders Iraq and where ISIS has been on the offensive since late April against rival jihadist and Islamist groups.

It comes as militants from the group seized an Iraqi crossing on the border with Syria after a day-long battle.

The Syrian army has stepped up its airstrikes against suspected ISIS positions in Syria in recent days in an apparent attempt to relieve pressure on the Iraqi army fighting the group in neighboring Iraq.

Meanwhile, Syria’s state-run news agency said a car bomb exploded in a government-held part of the northern Syrian city of Hassakeh, killing at least three people and wounding several others. It said the car was driven by a suicide attacker.