Jihadists killed in new push to take Syria

Syrian troops defending an air base have killed at least 24 rebels and wounded 150 others.

Syrian troops defending an air base have killed at least 24 jihadists in the province of Raqa. (AAP)

At least 24 jihadists have been killed and 150 wounded in clashes with Syrian troops defending an air base in Raqa province, a monitoring group says.

The clashes came on Saturday as the Islamic State group launched a new bid to capture the Tabqa base, the government's last bastion in the northern province, the rest of which is in the hands of the jihadists.

The Syrian Observatory for Human Rights said the attack began when a suicide bomber blew himself up at the entrance to the base, prompting clashes that killed 14 IS fighters.

The two sides exchanged rocket, artillery and heavy machine-gun fire, and the army deployed air strikes against the attacking jihadists, the Britain-based group said.

The air raids continued into the morning, with eight strikes against the town of Tabqa that killed 13 people, among them an additional 10 IS fighters.

Those deaths brought IS losses since it began its assault on Tabqa to at least 94, with more than 400 wounded, according to the Observatory.

IS has brought in reinforcements from other areas it controls in Syria, as well as neighbouring Iraq, the Observatory added.

The assault on Tabqa comes after IS seized the army's Brigade 93 and Division 17 posts in Raqa, killing dozens of soldiers, some of whom it beheaded.

The army has airlifted reinforcements to the base and stepped up air strikes against IS positions across Raqa, using both precision rockets and barrel bombs.