The Russian-backed Syrian army has crossed the border into Raqqa province, the heartland of ISIS, and there are reports they have promised to team up with US-backed rebel forces who share a common hatred of Daesh.

The Syrian Observatory for Human Rights said ISIS was retreating following Russian air strikes but there has been no confirmation from Moscow or the Assad regime in Damascus.

Some reports say the Assad regime has agreed to join forces with the Syrian Democratic Forces (SDF), a rebel group dominated by the Kurdish Popular Protection (YPG) militia.

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ISIS forces swept into Raqqa two years ago (pictured) but now they are said to be in retreat with the frontline only about 50 miles away

The SDF are said to have 30,000 fighters coming down from Kobani in the north.

ISIS is said to have around 5,000 fighters in Raqqa province and the city of the same name has been its de facto capital since it was taken in 2014.

The Syrian troops are said to be aiming at the Tabqa air base, 30 miles west of the city of Raqqa, which would give a base to Russian fighter jets.

The pro-Damascus newspaper Al-Akhbar in Lebanon said the short-term objective was Tabqa and nearby Lake Assad.

Malek Barghout (second from left) mourns the death of his father, who was killed in an air strike by Syrian government forces on the rebel-held neighbourhood of al-Sakhour in Aleppo. The fighting is extremely complex with the Assad regime, ISIS and other rebel forces at war with each other

ISIS is under attack on all sides.

In Iraq it is struggling to retain control of Fallujah following major advances by the Iraqi Army and allied Shia militias.

And in northern Syria the SDF rebels have advances towards Manbij, potentially closing off ISIS access to the Turkish border, which is a key supply line for them.

ISIS has lost 34 villages to the SDF and they are engaged in fierce battles for Marea, a town 50 miles west of Manbij.

'The fighting is very intense on three fronts in Marea,' said opposition activist Baraa al-Halaby.

Firemen douse the flames after Syrian government air strikes in Aleppo on Saturday

On Friday Russian jets bombed ISIS territory in neighbouring Hama province as Assad regime troops moved east.

Damascus radio said Syrian army troops gained ground and inflicted heavy casualties.

The London-based Syrian Observatory for Human Rights said 26 ISIS fighters had been killed along with nine from the Syrian army.

But the Syrian civil war remains hugely complex with the Nusra Front, an Islamist offshoot of al-Qaeda, having made gains against the Assad regime near Aleppo.

And dozens of people were reportedly hurt by Syrian government air strikes in Aleppo.