The landscape south of Raqa city strategically borders several provinces: Aleppo to the west, Homs to the south and Deir Ezzor -- much of which is still held by IS -- to the east.
Today, state news agency SANA said government loyalists had scored significant gains against IS in the area.
"Over the past two days, army units recaptured a number of villages and oilfields in western parts of Deir Ezzor province and southern parts of Raqa," the agency said.
The Syrian Observatory for Human Rights said today the government advance was backed by heavy Syrian and Russian air strikes.
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"Regime forces have captured between 1,500 and 1,800 square kilometres in Raqa province over the past 48 hours," Observatory head Rami Abdel Rahman said.
He said troops were approaching the strategic region of Jabal al-Bishri, a mountain chain straddling parts of Raqa, Deir Ezzor and Homs provinces.
"If the regime captures it, it can take control of all those areas," Abdel Rahman said.
But rival Syrian government troops have also chipped away at IS-held territory in the broader province.
Last month, regime forces targeted the US-backed Syrian Democratic Forces alliance west of Raqa. The Pentagon downed a Syrian jet in retaliation.
More than 330,000 people have been killed since Syria's conflict erupted in March 2011 with anti-government protests.