More than 600 people have been killed in Eastern Ghouta since the Syrian regime and its ally Russia intensified bombardment of the rebel enclave on February 18, a UK-based monitor said on Thursday.
The Syrian Observatory for Human Rights said of the 601 civilians, killed in mostly air strikes, 147 were children. It had previously reported 500 civilian deaths in Eastern Ghouta.
The rise in casualties came in part from the discovery of bodies that had remained trapped in the rubble of destroyed buildings by rescuers who took advantage of a Russian-brokered "humanitarian pause" to search for survivors.
The five-hour daily "pause" announced by Moscow on Monday has led to a reduction in the bombardment that killed hundreds in only a few days and sparked global outrage last month.
But a corridor offered by Russia for civilians to flee Eastern Ghouta appeared to be empty for a third day running, with distrust running high on both sides.
More than 40 trucks loaded with aid have been unable to reach the 400,000 people living in the battered enclave, prompting fresh calls for a United Nations ceasefire to be implemented.
However Jan Egeland, the head of the UN's humanitarian task force for Syria, said he hoped aid convoys "may now be able to go to Eastern Ghouta in the next few days".
He told reporters in Geneva that he had received word during a taskforce meeting on Thursday "that we may have the first facilitation letter, permit from the government, to go to [the main Eastern Ghouta town of]Douma in a very long time."
But he also stressed that "five hours is not enough".
Syrian aircraft carried out more air strikes on Thursday before the 9am start of the daily "truce", killing nine civilians, according to the Observatory.
Ground battles were also taking place in Al-Shaifuniyah which lies in the enclave's northeastern region and has been extensively destroyed in recent days.
A spokesman for the Syrian Civil Defence volunteer rescuers, known as the White Helmets, said access to the area had been very difficult.
"There is hardly any life there. It is completely destroyed and there are people under the rubble," Siraj Mahmud said.
Air strikes have eased compared with last week when the joint Syrian and Russian aerial campaign against Eastern Ghouta killed up to 100 civilians a day.
But the death toll for the assault launched on February 18 continued to mount even after Russia's "humanitarian pause" kicked in, as rescuers found bodies they had been unable to access.
In the town of Hazeh, rescuers working with rudimentary equipment were painstakingly hoisting buckets of gravel from a basement where they feared up to 21 were buried alive by a strike on February 20.
They have retrieved only six bodies so far.
"I left my daughter in the basement with her husband and his family," said 60-year-old Abu Mohamed.
"I came back the next morning. I found the building collapsed and until now I haven't found my daughter nor her husband's family."
According to the United Nations, three quarters of all private housing in Eastern Ghouta has been damaged and hundreds of civilian need life-saving medical evacuations.
The Russian daily "pause" falls far short of a 30-day ceasefire voted for by the United Nations Security Council on Saturday and which is yet to be implemented.
"When will your resolution be implemented?" top UN relief official Mark Lowcock asked Security Council members Wednesday.
Mr Lowcock said lorries loaded with supplies have been poised to go to 10 besieged areas, including Douma, since Saturday.
But he said there has been no access for humanitarian convoys, nor authorisation by the regime to go into the besieged areas, nor medical evacuations since the security council resolution was passed, he said.
On the contrary, the bombings have continued, and deaths and wounded have mounted, he said, speaking at a monthly council meeting devoted to the Syrian conflict.
Russia and its allies in Syrian president Bashar Al Assad's regime have blamed the humanitarian deadlock on the armed groups controlling Eastern Ghouta.
Syrian state media and military sources accused anti-regime forces in Eastern Ghouta of deliberately shelling the designated safe passage to prevent civilians from leaving and keep them as human shields.
A spokesman for Russian military observers monitoring the ceasefire initiative told Interfax news agency that many civilians were trying to leave.
The number of Ghouta residents asking for "assistance and help in getting evacuated from territory controlled by the fighters has increased exponentially over the past 24 hours," Major General Vladimir Zolotukin said.
However no movement was reported at the Wafideen checkpoint through which civilians were asked to evacuate the enclave.
The only civilians believed to have fled the enclave since the "pause" took effect are an elderly Pakistani couple who had remained in Ghouta throughout the seven-year conflict but decided to leave when the violence increased.
Mohammad Fadhl Akram, 73, moved to Syria in 1974.
He and his wife, who left on Wednesday and were given shelter at the Pakistani embassy in Damascus, left two sons, three daughters and 12 grandchildren behind.
"I hope God protects them," said Mr Akram. "I don't want anything else."