BEIRUT (Reuters) - The Syrian army has made a sudden advance against Islamic State in the desert area west of Raqqa, a military media unit run by its ally Hezbollah said on Tuesday.

Syria’s vast deserts have become the main theater of war in recent weeks as rival forces race to capture ground from the jihadist group, which is slowly retreating on several fronts.

The area between Ithriya and Tabqa, west of Islamic State’s de facto Syrian capital Raqqa, is important for the army since it can be used to attack government-held towns and supply routes.

According to the Hezbollah military media unit, the army has punched southwards to the Ithriya-Tabqa highway, a distance of about 20 miles (32 km) from its positions south of Maskaneh.

The road was used by Islamic State to attack positions along the government’s main supply route to Aleppo near Ithriya, and, if fully captured, would help the army advance into the desert.

It captured the villages of Rajm Askar, Bir Inbaj, Zahar Um Baj, Jab Aziz, Jab al-Ghanem, Abu Sousa and Jab Abyad from the jihadist group, the media unit said.

Syria’s army is aided in the six-year-long war by Shi’ite militias backed by Iran, including Lebanon’s Hezbollah, and by Russian air power.

A war monitor, the Britain-based Syrian Observatory for Human Rights, also said the Syrian army had advanced in that area. Al-Rusafa oil field is located nearby.

The advance will help the army to relieve pressure on the Ithriya-Khanaser road, part of the government’s supply route to Aleppo, the Observatory said.

The army has also launched attacks to push Islamic State back from the Salamiya-Ithriya road, part of the same supply route, in recent weeks.

The Syrian Democratic Forces (SDF), a group of militias backed by a U.S.-led coalition, holds Tabqa, northeast of the advances the army was reported to have made on Tuesday.

A week into its assault on Raqqa, the SDF on Monday reached the walls of the Old City from the eastern suburbs, the war monitor and a militia spokesman said. It is also pushing into Raqqa from the west and the north.