Russian-backed Syrian regime forces on Monday inched closer to a key stop on a vital
Islamic State (ISIS) group supply line, as a twin offensive bore down on the jihadists' northern stronghold.
The advance comes as 17 civilians — nearly half of them children — were killed in air raids on a popular market in eastern Syria on the first day of the holy Muslim month of Ramzan.
Government fighters entered the scramble for Tabqa at the weekend, when troops backed by Russian air strikes surged north towards the town on the banks of the Euphrates.
ISIS jihadists in the town of Tabqa are now caught between the regime forces advancing from the southwest and US-supported Kurdish and Arab fighters pushing in from the north.
The coincidence of the near-simultaneous attacks has raised speculation about possible coordination between the United States and Russia in the anti-ISIS fight.
The Syrian Democratic Forces (SDF), led by the
Kurdish People's Protection Units (
YPG ), last week launched an assault on Tabqa, its military base, and a nearby dam from the north of Raqqa province.
But while they remain 60 kilometres north of Tabqa, the government surged forward on Monday, said the Syrian Observatory for Human Rights.
Russian-backed government fighters are now within 24 kilometres of Lake Assad, the key reservoir in the Euphrates Valley contained by the
Tabqa dam , said the Britain-based Observatory.
Observatory head Rami Abdel Rahman said regime forces were "reinforcing their positions" south of the town.
"There is a joint operations room in Baghdad where the Iraqis and the Syrians are coordinating with the support of the Americans and the Russians," a source close to the regime said on Monday.
Around Tabqa in particular, the source said, it would be "impossible" for the US and Russia to back their respective ground allies if they did not coordinate.
London-based analyst Matthew Henman stressed that any coordination between Washington and Moscow has so far been "informal".
"There may be an element of informal, top-level coordination to avoid any confusion or inadvertent clashes but full coordination is unlikely," said Henman, who heads IHS Jane's Terrorism and Insurgency Research Centre.
Russia last month floated a proposal for joint air strikes with the US against jihadists in Syria, but the offer was swiftly rejected.
Two years after it shot to international infamy after declaring a fundamentalist "caliphate," ISIS is coming under mounting international pressure.
