East Ghouta is one of the few areas in the country still under rebel control
The UN says there has been an 'extreme escalation' of hostilities in the Eastern Ghouta area of Syria.
Scores of people have been killed and injured in recent days, according to monitoring groups and local rescue teams.
Eastern Ghouta - which is around 15 kilometres from Damascus city centre - has been besieged by the Syrian army since 2013, and it is one of the few areas in the country still under rebel control.
The last few weeks have seen the area targeted by Russia-backed Syrian government forces.
Last night, Syria Civil Defence - also known as the White Helmets - said more than 100 civilians, including 20 children, had been killed over 24 hours.
This morning, they reported that strikes had continued, with at least two dozen civilians killed.
Civil Defense teams worked to rescue a baby, and a panic among civilians after the renewed aerial bombardment on residential neighborhoods in #Douma city in #EastrenGhouta. #SaveGhouta pic.twitter.com/1umEHaiiqa— The White Helmets (@SyriaCivilDef) February 20, 2018
Direct targeting of #CivilDefense teams while there work to evacuat the civilians and wounded from air strikes areas in #Mesraba city in #EasternGhouta. #SaveGhouta #GhoutaGenoside pic.twitter.com/CzESp3W0WY— The White Helmets (@SyriaCivilDef) February 20, 2018
Panos Moumtzis, the UN's Regional Humanitarian Coordinator for the Syria Crisis, said he was alarmed by the escalation of hostilities - confirming that more than 40 civilians had been killed and 150 injured on Monday.
Mr Moumtzis said access to East Ghouta is 'woefully inadequate', with no aid convoys having taken place in December and January.
In a statement, he said: "The recent escalation of violence compounds an already precarious humanitarian situation for the 393,000 residents of East Ghouta, many of them internally displaced, and which account for 94% of all Syrians living under besiegement today.
"The humanitarian situation of civilians in East Ghouta is spiraling out of control. It’s imperative to end this senseless human suffering now. Such targeting of innocent civilians and infrastructure must stop now."
The conflict in Syria has seen more than 300,000 people killed and millions more displaced since it began in early 2011.