Syria's regime sent reinforcements to Eastern Ghouta on Wednesday, tightening the noose around the shrinking rebel enclave hours before a top-level UN meeting on the escalating violence.
The blistering onslaught has prompted outrage against the regime, with the United Nations' human rights chief saying the government was orchestrating an "apocalypse" in Syria.
The Russia-backed Syrian army and allied militia launched an offensive on February 18 to retake the last opposition bastion near Damascus.
They have since taken more than 40% of the enclave, waging a devastating bombing campaign that has killed more than 800 civilians.
Heavy air strikes battered several key towns in the zone on Wednesday, as Syria's government dispatched hundreds of pro-government militiamen to the front.
"At least 700 Afghan, Palestinian, and Syrian loyalist militiamen came from Aleppo and were sent late Tuesday to Ghouta," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
The Britain-based war monitor said the reinforcements were deployed to two main battlefronts on the western side of the enclave, including the town of Harasta.
Government troops on Wednesday were within firing range of the key towns of Misraba and Beit Sawa, and had taken up positions at the edges of Jisreen and Hammuriyeh.
Three civilians including one child were killed in heavy air strikes on Jisreen on Wednesday, the Observatory said.
That brought the toll in more than two weeks of bombing to 810 civilians, including 179 children.
Syria's state television on Wednesday morning showed a live broadcast of farmland adjacent to Misraba, with columns of smoke emerging from the town's skyline.
The bombardment has continued despite a one-month ceasefire demanded by the United Nations Security Council more than a week ago.
The council will meet behind closed doors on Wednesday afternoon to discuss the failed truce, after France and Britain requested urgent talks.
UN human rights chief Zeid Ra'ad Al Hussein said the Syrian regime and its foreign allies were already planning their next "apocalypse."
"This month, it is Eastern Ghouta which is, in the words of the Secretary General, hell on earth; next month or the month after, it will be somewhere else where people face an apocalypse -- an apocalypse intended, planned and executed by individuals within the government, apparently with the full backing of some of their foreign supporters," said Hussein.
Eastern Ghouta's roughly 400,000 residents have lived under government siege since 2013, facing severe shortages of food and medicines even before the latest offensive began.
Forty-six aid trucks entered the area on Monday for the first time since the offensive, but had to cut short their deliveries and leave due to heavy bombardment.
Nearly half of the food aid could not be delivered and Syrian authorities removed some medical and health supplies from the trucks, the UN said.
Secretary-General Antonio Guterres urged all warring sides to allow aid trucks to return for a planned second delivery to the enclave's main town of Douma on Thursday.
Linda Tom, spokesperson for the UN's humanitarian coordination office OCHA in Syria, said the aid would aim to reach 70,000 people in Douma and would include medical supplies not allowed in Monday's delivery.