The advances toward the provincial boundary between Raqqa and Deir al-Zor took place late on Saturday, the media unit, run by Damascus ally Lebanese Hezbollah, and the British-based Syrian Observatory for Human Rights said.
The army seized an oilfield in the Sabkha area as part of the advance, Reuters reported.
It was a rare advance for Damascus's forces in that area, which is close to territory controlled by the US-backed Syrian Democratic Forces (SDF). It also brings government forces closer to Deir al-Zor Province, another Daesh stronghold.
The Syrian Army has active frontlines with Daesh in western Raqqa province and has made recent gains there.
Incidents between the Syrian military and SDF last month raised tension between Washington and Damascus and its ally Moscow.
Separately in the north of Syria, one of the country's most complicated battlegrounds, Turkish-backed Syrian forces are fighting US-backed Kurdish forces over control of some areas along the border, in clashes that threaten to distract from the fight against Daesh.
PressTV News Videos Published on Jul 18, 2017 The Syrian army and its allied units are blasting their way toward the Daesh stronghold of Raqqah, making fresh gains against the terrorist group.