The Syrian Observatory for Human Rights says regime airstrikes in the region have intensified over the past few weeks, causing civilian casualties.
Renewed Syrian regime bombardment of rebel-held Eastern Ghouta outside Damascus on Monday killed at least 18 people, including two children, despite a ceasefire deal for the region, the Syrian Observatory for Human Rights says.
Eastern Ghouta, one of the last remaining opposition strongholds in Syria, is among four so-called "de-escalation zones" set up earlier this year under a deal agreed by regime allies Russia, Iran and Turkey.
But despite the agreement, violence has spiralled in the area in recent days.
It said at least 45 others had been wounded, and the death toll could rise because a number of the injured were in a serious condition.
French medical humanitarian organisation Doctors Without Borders (MSF) said Monday the constant bombardment was resulting in "huge numbers of wounded, reduced medical capacity and creating a disaster for patients in need of treatment".
Russia proposes ceasefire
Russia proposed a two-day ceasefire on Monday in the last major rebel stronghold near the Syrian capital Damascus, where warplanes killed dozens of in two days of air strikes as Russian-backed regime forces tried to capture the area.
Russia proposed imposing a ceasefire in the de-escalation zone for Tuesday and Wednesday, Interfax news agency reported, quoting the Defence Ministry.
"Such measures will ease tension in the western part of the de-escalation zone," General-Lieutenant Sergei Kuralenko, in charge of Russia's ceasefire monitoring centre in Syria, was quoted as saying.
Cries of pain at field clinic
At a field clinic in the city of Douma, which has regularly come under government attack, medics worked with the limited supplies available to them to treat waves of arriving injured.
The wails of a distraught mother could be heard along with the low moans of a wounded man who rocked back and forth in pain on a white hospital bed.
A young boy waited to be treated, the leg of one trouser pulled up to reveal a bloodied wound on his left shin.
One medic, wearing thin, loose transparent plastic gloves usually used by grocers rather than standard medical-grade ones, wrapped gauze around the head of another boy whose face was red with blood.
Elsewhere, some of the bodies of those who could not be saved were wrapped in light blue sheets tied with white strips of fabric at the ankles, waist and head.
Others who had yet to be wrapped up were still lying on a bloodied tile floor in another part of the clinic, where one man wept openly, his left hand bandaged.
The deaths come a day after at least 23 civilians were killed in the region in regime air strikes and artillery fire, among them four children.
Over 100 killed in two weeks
The Observatory says regime bombardment of Eastern Ghouta has killed more than 100 people in the past two weeks.
Rebels have also fired from the area into Damascus in deadly attacks of a kind rarely seen in the capital.
MSF said that between November 14 and 26, five field hospitals it supports in Eastern Ghouta had "responded to 24 mass casualty influxes".
It said the toll over the 13 days at those facilities was 69 dead and 576 wounded, a quarter being women and children.
Eastern Ghouta is already in the grip of a humanitarian crisis caused by a crushing regime siege of the area since 2013 that has caused severe food and medical shortages.
Humanitarian access to Eastern Ghouta has remained limited despite the implementation of the ceasefire zone, and a United Nations official has named the region as the "epicentre of suffering" in Syria.
On the political front, peace talks set to open in Geneva Tuesday hit a hurdle as President Bashar al-Assad's government refused to confirm its attendance, instead telling the UN no delegation would arrive on Monday.
More than 340,000 people have been killed in Syria since its conflict began in March 2011 with anti-government protests.