New air strikes and barrel bombs pounded Syria's Eastern Ghouta on Sunday as government forces pressed a three-week advance that splintered the rebel enclave and trapped dozens under collapsed buildings.

Defying global calls for a ceasefire, Syria's government has pursued a ferocious Russian-backed air campaign and ground offensive to capture the region, the last rebel bastion on the capital's doorstep.

In three weeks of fighting, it has overrun more than half the area and split the remainder into three pockets, isolating the urban hub of Douma from the rest of the enclave.

On Sunday, government troops battered the edges of each pocket with air raids, barrel bombs, and rockets, according to the Syrian Observatory for Human Rights (SOHR).

“The clashes are focused now around the town of Medeira, which lies at the centre of the three zones and where rebels are putting up fierce resistance,” said Observatory head Rami Abdel Rahman.

Bombing runs hit several other towns including Arbin, where at least three civilians were killed.

The deaths bring the total toll from the offensive to at least 1,102 civilians, according to the monitor.

They include dozens of decomposing bodies still trapped under pulverised residential blocks in the towns of Hammuriyeh, Saqba, and Misraba.

In Hammuriyeh, AFP's correspondent saw a young man scrambling frantically over the rubble of a collapsed building in search of his loved ones.

His father, mother, and three siblings were killed in an air raid, but rescue workers have been unable to pull them out.

Bodies pile up

Hassaan, a 30-year-old rescue worker, said there were around 20 more families under the rubble.

“We need heavy machinery to get them out, but we can't bring the machines out into the streets because the regime may bomb them,” he said.

In the main town of Douma, bodies piled up in the morgue as bombardment prevented families from reaching the cemetery, AFP's correspondent there said.

Families grew desperate for news of loved ones who had fled to other areas that were now inaccessible.

On Saturday, Syrian troops and allied militia cut off the main road leading out of Douma in a major blow to beleaguered rebels attempting to defend their enclave.

Government forces also captured the town of Misraba.

Some residents fled from the advancing troops, but dozens stayed as soldiers recaptured their neighbourhoods.

Syrian state news agency SANA reported on Sunday that troops transported “dozens of civilians, including women and children,” from Misraba to temporary shelters in government-held zones.

The Observatory told AFP that Misraba was left abandoned after 75 to 100 people were moved out of the town by regime forces.

Syrian President Bashar al-Assad is keen to recapture Eastern Ghouta from rebels, who have used the region as a launch pad for attacks on the capital.

In recent years, government forces and pro-regime militias have recaptured several areas around Damascus and other parts of war-ravaged Syria from rebels by pursuing fierce military offensives culminating in evacuation deals.

Officials mull evacuation

Officials from Hammuriyeh were on Sunday considering such an evacuation after talks with the regime, a negotiator and the Observatory told AFP.

A delegation from the town met government representatives on Saturday and discussed a proposal that would offer safe passage to rebels and civilians who want to leave, a member of the Hammuriyeh delegation said.

“The committee is meeting on Sunday to take a decision and inform the regime,” the delegate told AFP on condition of anonymity.

The Observatory confirmed talks were taking place on Hammuriyeh as well as the towns of Jisreen and Saqba.

The two main rebel groups in Eastern Ghouta have firmly and repeatedly denied negotiating with the Syrian regime.

Faylaq al-Rahman, the opposition faction that holds Hammuriyeh, insisted late on Saturday there were “no direct or indirect negotiations” on an evacuation.

Eastern Ghouta is home to around 400,000 people living under a crippling government siege since 2013.

The United Nations has demanded a month-long ceasefire there to allow for aid to be brought in and for desperately sick and wounded civilians to seek treatment.