Farther south, in an area newly cut off from Douma, protests have proliferated. Residents are demanding that rebels leave, hoping that their departure would eliminate the main reason for the government bombings. On Monday, rebel fighters fired on demonstrators, killing one, a local doctor said.
It was an unusual turnabout, almost exactly seven years after the Syrian uprising began as peaceful demonstrations that later transformed into an armed rebellion after security forces fired on protesters.
The government advance and the preceding years of bombardment have all but demolished most of eastern Ghouta. Despite a cease-fire endorsed two weeks ago by the United Nations Security Council, attacks have only intensified as the government seeks to reclaim the area.
Expressing exasperation, the American ambassador to the United Nations, Nikki R. Haley, said Monday that the cease-fire had failed and that the United States might take unspecified action of its own. “It is not the path we prefer, but it is a path we have demonstrated we will take and are prepared to take again,” Ms. Haley told the Council. What precisely she had in mind was unclear.
Although Russia announced the opening of two humanitarian corridors to the north and the south of the enclave, the bombardment has scarcely subsided to allow civilians safe passage. There have been reports of government forces detaining or summarily killing people in retaken areas, and of rebel snipers shooting civilians trying to reach the government side.
On Monday, the Army of Islam, a hard-line Islamist group that holds the northern block of eastern Ghouta, issued a statement announcing an agreement with Russia and the United Nations to evacuate some wounded for treatment, in batches.
More than 1,000 civilians have been killed in the onslaught since the escalation of the Syrian government’s campaign to take eastern Ghouta began last month. The United Nations has said 1,000 civilians need urgent medical evacuation.
Accounts have multiplied of families and friends abruptly separated by the quickly shifting front lines.
Mr. Habaq and his family, from the town of Arbin, had moved to his wife’s parents’ house in nearby Harasta in late February after his house was bombed. But with Harasta under intense bombardment and its fall to Syrian government forces imminent, he left for the suburb of Zamalka — slightly farther from the front line — to scout for a shelter where he could move his family.
On Monday it looked as though he might never see them again.
“They are not far, but I can’t reach them,” he said in a voice message — the road was too treacherous. “It’s like doomsday.”
Zamalka, where Mr. Habaq was hoping to find a safer place for his family, is not much better: He said civilians had crowded there “like pickles” in a jar, some sleeping in the streets, under stairwells and in fields.
Desperation punctuates life for the 393,000 civilians who remain in eastern Ghouta, according to United Nations estimates. Many have spent weeks in underground shelters.
Huda Khayti, who runs a center for psychological and social support for women in Douma, said she lost her brother last week after he emerged to retrieve water for everyone in their shared underground shelter.
“We have children who haven’t seen light or sun in more than 20 days,” Abu al-Nasser, a doctor who uses a pseudonym for safety, said in an online message.
With the bombings, diminished food and medical supplies and internal rifts between rebel groups, residents have begun expressing frustration in new ways.
Civilians in the eastern Ghouta towns of Kafr Batna and Hammouriyeh have held a spate of protests calling for rebel groups to leave.
On Monday, Syrian state television showed hundreds of people in Kafr Batna and nearby villages demonstrating, holding the Syrian flag and chanting: “We don’t want freedom. We want national unity.”
Civilians there hope that if the rebel groups make a deal to leave the area, they can be free of bombardment without leaving their homes.
But masked snipers opened fire on protesters in the street from nearby buildings, killing one and wounding six, according to the Syrian Observatory for Human Rights, a Britain-based group that monitors the war through contacts on the ground.
That part of eastern Ghouta is partly controlled by Faylaq al Rahman, an Islamist rebel group that calls itself part of the Free Syrian Army. Fighters from the Levant Liberation Committee, which has links to Al Qaeda, are also there.
The account of the shooting was confirmed by a local doctor, Ahmad al-Bukai.
“I understand that people at this stage don’t care if the regime takes Ghouta,” he said in a phone interview. “I don’t think the two widowed, bereaved women I am treating here in the field hospital are thinking of freedom after losing their husbands and kids.”
Working in eastern Ghouta from the start of the rebellion, Dr. Bukai said he had been detained three times by security forces and once by the Qaeda group, and witnessed the chemical attack in 2013 that killed about 1,400 people.
“Almost about the same number, 1,400, is the death toll over the past 25 days,” he said. The brutality of the Syrian regime is still the same.”
He also blamed rebel infighting. “What we are living now is the result of the differences among all rebel groups and their agendas,” he said.
But rebel groups have refused to surrender, despite reports of negotiations.
Mr. Habaq finally reached his family on Monday afternoon. He took a risky journey across the front line to guide them from Harasta to Arbin, where, as of Monday night, they were hiding — in the old, bombed-out home they fled from last month — until it was safe to find a better shelter.