Airstrikes hit Syria's Eastern Ghouta for a third straight day on Tuesday (February 20th), bringing the civilian death toll to nearly 200 as the UN warned the situation in the opposition enclave was spinning "out of control".

Airstrikes and rocket and artillery fire have battered the opposition-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 airstrikes on Tuesday morning killed at least 50 civilians, including 13 children, the monitor said.

Held by the oppositon since 2012, Eastern Ghouta is the last opposition pocket around Damascus.

The UN's regional humanitarian co-ordinator 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 is imperative to end this senseless human suffering now," Moumtzis said on Monday.

The UN has repeatedly called for a month-long ceasefire across Syria's front lines, from Eastern Ghouta to Afrin in the north-west, which Turkey has threatened on Tuesday to lay siege to in the coming days.

'No words'

"February 19th was one of the worst days that we have ever had in the history of this crisis," said an exhausted doctor in a hospital in Eastern Ghouta.

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-Yasar told AFP.

He pulled out the dirt as fast as possible, put in the breathing tube and managed to save the baby's life.

"This is just one story from among hundreds of wounded."

The bloodshed prompted the UN children's agency UNICEF to issue a largely blank statement on Tuesday to express its anger.

"We no longer have the words to describe children's suffering and our outrage," the agency said in a brief postscript beneath the empty space on the page.

"Do those inflicting the suffering still have words to justify their barbaric acts?"

More than 400,000 people live in Eastern Ghouta, which has been surrounded by government troops since 2013. Food, medicine, and other basic necessities are nearly impossible to obtain.