Troops on Monday reached within 24 km (15 miles) of Lake Assad, the key reservoir in the Euphrates Valley contained by the Tabqa Dam, said the Syrian Observatory for Human Rights.
The London-based monitor’s head Rami Abdel Rahman said Syrian government forces were “reinforcing their positions” south of the dam which is 40 kilometers from Raqqa.
The Syrian Democratic Forces (SDF), a coalition of Kurdish and Arab fighters, were also moving toward the dam, but are further away due to their focus on the liberation of Manbij, it said.
On Saturday, the Syrian army entered Raqqa Province for the first time since 2014, when ISIS unleashed its ferocious campaign of terror in the Arab country.
The potential recaptures of the city of Raqqa in Syria, and the Iraqi city of Mosul are seen as the ultimate blows to ISIS.
In Iraq, security forces have reportedly edged as close as 30 kilometers (18 miles) to Mosul, which is the capital of Nineveh Province.
On Monday, Russia pledged firm aerial support for Syrian operations against ISIS and al-Qaeda-linked Nusra Front in Aleppo.
“We will be actively supporting the Syrian army from the air to prevent terrorists from seizing territory,” Russia’s Foreign Minister Sergei Lavrov said.
He also dismissed Washington’s insistence on the suspension of the airstrikes against the terrorists so that the US-backed “moderate” militants can leave the city.
Washington “is asking us and Syrian leadership to delay airstrikes” until the militants are separated from the terrorists, Lavrov said. “We believe there has been more than enough time (for that.”
On Friday, Lavrov said The US had asked Russia to stop conducting airstrikes against Nusra Front terrorists in Syria.
“They are telling us not to hit (Nusra), because there is ‘normal’ opposition next … to it,” Lavrov said. “But that opposition must leave terrorists’ positions, we long have agreed on that.”
Al-Nusra and other Takfiri terrorists hold most of the northwestern province of Idlib and parts of neighboring Aleppo province.
Last week, the Syrian Observatory for Human Rights said Nusra Front has recruited 3,000 new militants, including teenagers, since March in comparison to an average of 200 to 300 a month before.
Other sources said hundreds living in camps for displaced people in the northern parts near Turkey have joined the terrorist al-Qaeda branch in Syria, the Associated Press reported.
Syria has been gripped by militancy since March 2011. UN special envoy for Syria Staffan de Mistura estimates that over 400,000 people have been killed in the conflict.