Updated

Syrian government warplanes carried out at least eight strikes Sunday against Islamic State militants attacking a key military air base in eastern Syria, activists said.

The Islamic State group launched its assault on the sprawling air field just outside of the city of Deir el-Zour last week, touching off fighting that activists say has killed more than 150 people on both sides. For IS, seizing control of the base would eliminate the last significant government presence in the area and provide a major morale and propaganda boost.

The Local Coordination Committees activist collective and the Britain-based Syrian Observatory for Human Rights said Sunday's airstrikes targeted four areas near the base.

After IS fighters succeeded in storming part of the base, the Syrian military on Saturday launched a counterattack -- bolstered by heavy air raids -- to push the militants back. Scattered clashes on the ground continued Sunday with fighting on several fronts around the base, activists said.

A Syrian military official in Damascus told The Associated Press that troops are in full control of the base.

"They (IS) tried to launch attacks from their positions around the airport but they were countered, and tens of them were killed and large amounts of weapons were seized," he said, speaking on condition of anonymity because he was not authorized to brief the media.