Syrian government troops and allied fighters captured some of the last parts of Deir Ezzor city from the Islamic State group on Thursday, state media and a monitor said.

Syria's army has been battling inside the city since September, when it broke a jihadist siege of nearly three years on government-held parts of the provincial capital.

The jihadist group is facing the prospect of another major loss after a string of setbacks, including being ousted last month from its one-time de facto Syrian capital Raqa.

Syrian state media said Thursday that the army and allied fighters had captured three neighbourhoods in the city, and "tightened the siege" on IS fighters in several remaining districts.

State news agency SANA said IS fighters were using loudspeakers to urge remaining members of the group "not to run away from the fighting, and to kill any member who tried to escape or surrender".

The Britain-based Syrian Observatory for Human Rights monitor also reported the regime advances in the city, provincial capital of Deir Ezzor, on Syria's eastern border with Iraq.

The monitor said government forces were advancing as ally Russia carried out heavy air strikes in support of the offensive.

"If the regime's forces succeed in continuing this offensive, they could bring an end to IS's presence (in the city) in hours or days," the Observatory said.

On the ground, a journalist contributing to AFP saw widespread destruction during a tour of neighbourhoods recently recaptured by the army.

Entire floors of buildings had crashed onto those beneath, while others had their facade completely blown away, revealing empty, destroyed interiors.

Trenches dug by IS fighters were still visible, as were army minesweepers working to locate and defuse explosives laid by the jihadists.

- 'Female suicide bomber' -

On the outskirts of remaining IS-held territory, soldiers fired from tanks.

A warplane roared overheard and carried out a strike that sent a large cloud of grey smoke above the city's skyline of damaged buildings.

"The Syrian army controls more than 80 percent of the city," a military source said, speaking on condition of anonymity.

"Daesh is scrambling to defend its last positions, which the army is continuing to advance on until they are eliminated completely," the source said, using the Arabic acronym for IS.

He added that the jihadists were using vehicle bombs and snipers, and alleged they were "sending female suicide bombers" to target army positions.

IS once held large sections of Deir Ezzor city, and for nearly three years laid siege to other parts of it that remained under government control.

In early September, advancing government forces broke the siege, and they have been working since to expel the jihadists from the rest of the city.

A local source said between 150-200 civilian families were estimated to remain in areas held by IS in the city.

The military source said operations were slowed at times to allow searches for civilians and their evacuation.

Oil-rich Deir Ezzor province was once an IS stronghold, but the jihadist group now faces twin assaults there, from the regime and the US-backed Kurdish-Arab Syrian Democratic Forces.

The jihadists have already been expelled from neighbouring Raqa province, and are now confined to just a few pockets of territory in Deir Ezzor.

More than 330,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests