The Syrian army and rebel groups have fought fierce battles on a critical front in eastern Ghouta where government advances have in effect splintered the insurgent enclave near Damascus into three.
State television on Sunday broadcast from the edge of the eastern Ghouta town of Mudeira, where an army field commander told Reuters pro-Syrian government forces had arrived earlier in the day.
Footage showed several massive plumes of smoke in the distance behind a war-ravaged townscape with big holes in walls and roofs, and yet more smoke wafting across the streets. The sound of blasts could be heard.
The Syrian Observatory for Human Rights said there was intense fighting on several fronts accompanied by a government artillery barrage, continuous air raids and attacks by helicopters.
The Syrian army has completely surrounded the major town of Douma after advancing from Mesraba to Mudeira, two other towns in the area, a military media unit run by the government's ally Hezbollah said on Sunday.
That army advance met up with another from the area around the town of Harasta, cutting the remaining rebel area in eastern Ghouta in two, it said.
Rebel groups in eastern Ghouta have vowed they will fight on. A statement issued by Free Syrian Army factions there late on Saturday said they had taken a decision not to accept a surrender and negotiated withdrawal.
Syrian state media also reported army advances near Jisreen and Aftaris in the southeastern part of the rebel-held territory.
Syrian President Bashar al-Assad and his ally Russia see the rebels as terrorist groups, and say their offensive is needed to end the rebels' rule over eastern Ghouta's large population.
But the violence of their assault has prompted condemnation from Western countries and repeated calls by United Nations aid agencies for a humanitarian ceasefire.
Activists and fighters in eastern Ghouta in recent days have said the bombardment has included incendiary material that causes fires and burn injuries. Local doctors have also reported several incidents of bomb attacks followed by the smell of chlorine and choking symptoms.
The government denies using either incendiary weapons or chemical weapons, and said on Saturday it had information that the rebels were planning to stage a fake chemical attack to discredit the army.
In Muscat, US Defense Secretary Jim Mattis said it would be "very unwise" for Syrian government forces to use weaponised gas, citing the unconfirmed reports of chlorine attacks in eastern Ghouta.