Syrian state media reports say the military and allied forces are closing in on the eastern city of Deir al-Zour, which has been besieged by the extremist group Islamic State (IS) for three years.

State television said on September 4 that the advancing forces were within 3 kilometers of the government enclave, while the news agency SANA reported the "collapse" of IS defenses in the area.

A military media unit run by the Lebanese Shi'ite Hizballah movement said they were heading to the besieged garrison's camp on the city outskirts.

The Russian Defense Ministry said its air force was providing aerial support to the offensive.

IS controls half of Deir al-Zour, the center of Syria's oil industry, and most of its surrounding province.

It is the IS group's last major stronghold in Syria, with the de facto capital of Raqqa under siege by a U.S.-backed alliance of Syrian Kurdish and allied Arab fighters.

The United Nations estimated in August that 93,000 civilians were living in the government enclave in Deir al-Zour, which has been supplied via air drops.

Based on reporting by Reuters, AP, and Interfax