The Syrian army intensified its onslaught in Eastern Ghouta with advances that a war monitor and state media said had splintered the enclave, though a rebel official denied this.
Syrian state television broadcast from inside the town of Mesraba, a town along the road connecting the northern and southern halves of the rebel-held enclave, after reporting that the army had taken it earlier on Saturday.
The capture of Mesraba and advances into nearby farmland brought important roads directly under fire by the army, the Syrian Observatory for Human Rights said.
That has in effect cut the large towns of Harasta and Douma off from each other and the rest of the enclave, it added.
However Hamza Birqadar, a spokesman for Jaish al-Islam, one of the two main insurgent groups in Eastern Ghouta, said rebels had repelled the attack on Mesraba and neither Harasta nor Douma were cut off.
The three-week assault on the last major rebel stronghold near Damascus has captured about half its area and killed 976 people, according to the Britain-based Observatory.
State television showed a massive plume of dark smoke rising behind houses and trees in Eastern Ghouta, with the sound of blasts in the background.
Syrian President Bashar al-Assad and Russia, his main ally, say the campaign is needed to end rebel shelling of Damascus and to end the rule of Islamist insurgents over the area's civilians.
The offensive follows the pattern of previous assaults on rebel strongholds, deploying massive air power and tight sieges to force insurgents to accept "evacuation" deals.
These involve rebels surrendering territory in exchange for safe passage to opposition areas in northwest Syria, along with their families and other civilians who do not want to come back under Assad's rule.
Late yesterday, a small number of fighters and their families from the former al Qaeda affiliate previously known as the Nusra Front left Eastern Ghouta under such a deal.
But the group represents only a small portion of the insurgent presence in the enclave, and both Jaish al-Islam and the other main Eastern Ghouta rebel group Failaq al-Rahman have said they are not negotiating a similar deal for themselves.
The intensity of the government's attack on an enclave that has been besieged since 2013 and suffers acute shortages of food and medical supplies has drawn western condemnation and demands by UN aid agencies for a humanitarian halt in fighting.
The United Nations estimates that some 400,000 people are trapped in Eastern Ghouta.
Aid agencies have tried to deliver supplies into Eastern Ghouta, but they have only been able to bring in a portion of the amount they wanted.
A convoy was unable to finish unloading on Monday because of continued fighting, bringing in the remaining undelivered food parcels on Friday despite bombardment nearby.
However, UN agencies said most medical supplies had been stripped from the convoy by Syrian government officials and added that the food supplies brought in were insufficient.
Medical charities have reported several incidents in recent weeks of what they say was chlorine gas use in government bombardments, causing choking symptoms.
On Saturday, Syria's deputy foreign minister, Faisal Mekdad, rejected those charges and accused the United States of orchestrating the accusations in order to support militant groups.
"We did not deny a single request for investigation," Mekdad told a news conference.
The government has opened what it says are several safe routes out of Eastern Ghouta for civilians, but none are known to have left so far and Damascus and Moscow accuse the rebels of preventing them from fleeing the fighting.
Insurgent groups in Eastern Ghouta deny this, saying people have not left for fear of government persecution.