A Syrian man carries a wounded infant at a makeshift hospital in the rebel-held town of Douma, in Eastern Ghouta, on Tuesday.
Held by rebels since 2012, Ghouta is last opposition pocket near Damascus.
Air strikes hit Syria's Eastern Ghouta for a third straight day on Tuesday, bringing the civilian death toll to nearly 200 as the UN warned the situation in the rebel enclave was spinning "out of control".
Air strikes and rocket and artillery fire have battered the rebel-held enclave since Sunday in apparent preparation for a government ground assault on the besieged region.
At least 194 civilians have been killed, among them 57 children, the Syrian Observatory for Human Rights said.
On Monday alone, 127 civilians, including 39 children, were killed in the bombardment - the single bloodiest day for Eastern Ghouta in four years.
Fresh air strikes on Tuesday morning killed at least 50 civilians, including 13 children, the Britain-based war monitor said.
Held by rebels since 2012, Eastern Ghouta is the last opposition pocket around Damascus and President Bashar Al Assad is keen to retake it with an apparently imminent ground assault.
The UN's regional humanitarian coordinator for Syria Panos Moumtzis has warned that the targeting of civilians in the enclave "must stop now".
"The humanitarian situation of civilians in East Ghouta is spiralling out of control. It's imperative to end this senseless human suffering now," Moumtzis said.
The UN has repeatedly called for a month-long ceasefire across Syria's front lines, from Eastern Ghouta to the Kurdish enclave of Afrin in the northwest, which Turkey threatened on Tuesday to lay siege to in the coming days.
"February 19 was the one of the worst days that we've ever had in the history of this crisis," said an exhausted doctor.
Identifying himself as Abu Al Yasar, he described treating a one-year-old brought into the Arbin hospital with blue skin and a faint pulse, rescued from under the rubble.
"I opened his mouth to put in a breathing tube and I found it packed with dirt," Abu Al Yaar told.