Syria's regime moved closer Sunday to fully retaking the rebel enclave of Eastern Ghouta after its Russian ally agreed with rebels to evacuate hundreds of civilians from a final pocket.

Tens of thousands people are thought to remain in the battered town of Douma, the last rebel holdout and their one-time bastion east of the capital Damascus.

Russia-backed regime forces have seized more than 95 percent of Eastern Ghouta in a six-week air and ground blitz that has displaced tens of thousands from their homes.

People have fled the fighting into regime-held territory, while so far more than 45,000 fighters and civilians in total have been bussed out under evacuation deals.

"A partial agreement was reached to evacuate hundreds of civilians who wish to leave for Idlib", a northwestern province still largely outside regime control, a Britain-based war monitor said on Sunday.

In all, around 1,300 people would be evacuated from Douma under the deal, the head of the Syrian Observatory for Human Rights told AFP, adding that talks on the fate of rebels who hold Douma were still underway.

"Negotiations were continuing for a full agreement, including concerning the Jaish al-Islam" rebel faction, Rami Abdel Rahman said.

In other parts of the bastion, Russia-brokered accords have already seen thousands of fighters and civilians climb onto buses and head north to Idlib.

More than 4,000 people left the devastated town of Harasta last week under a deal with the Ahrar al-Sham rebel group.

And more than 41,000 evacuated a southern pocket including the town of Arbin this week under another deal with the Faylaq al-Rahman opposition faction.

But talks have dragged on in Douma, with Jaish al-Islam insisting it would not leave the town, the main one in Eastern Ghouta.

A civilian committee taking part in the negotiations with Russia on Saturday said a deal had been reached "to evacuate humanitarian cases to northern Syria".

It gave no further details nor did it say when the planned evacuations would start.

As talks have stalled for Douma, residents there have grown nervous about their fate.

"Of course I would rather leave. There are no more homes here, not a single place to settle," said Abu Rateb, 30.

"But I won't go to regime-held areas to join ranks with the Syrian army," he said, adding he would prefer to go to Idlib.

Haitham, 38, a media activist who did not give his surname, said he would rather stay in his hometown.

"To abandon your home is to abandon your soul," he said.

"But if they give us the choice of dying or leaving, it will be another matter."

Reports of the planned evacuations come after Syria's army on Saturday vowed to finish off rebels in Douma, the main town in Eastern Ghouta.

A statement said the military would press on with "fighting in the area of Douma to rid it of terrorism", in reference to the rebels.

That announcement came after Syria's state news agency SANA reported the southern pocket of Eastern Ghouta was "empty of terrorism" as the last buses left it on Saturday afternoon.

The regime assault since February 18 has killed more than 1,600 civilians, the Observatory says, and devastated entire neighbourhoods.

Tens of thousands of people have hit the roads, with their belongings stuffed into bags or carrying blankets, to flee out of the enclave into regime-held territory.