"Troops and pro-government militia stopped the attack that ISIS launched on the Deir Ezzor military airport," the Syrian Observatory for Human Rights said, adding that both sides suffered heavy losses in the fighting.
The terrorrists had withdrawn to the edges of the base, a day after managing to seize a southeastern part of the complex, it said.
The Observatory said more than 100 terrorrists had been killed in fighting for the base since Wednesday, when they launched an operation to try to take the airport.
The Deir Ezzor air base is a key outpost from which warplanes and helicopters mount raids on terrorist positions in several areas of the country.
The oil-rich province lies between ISIS-controlled Raqa province and the border with Iraq.
Yesterday, Reinforcements arrived in Deir Ezzur airport East of Syria for the national military following the gunmen attack on Thursday.
ISIS group terrorists have stormed parts of a army air base after days of clashes that killed dozens.The Britain-based Syrian Observatory for Human Rights says yesterday the latest attack began Saturday with a suicide car bomb on the main entrance of the Deir el-Zour air base.