- 310 have been killed in Eastern Ghouta since Sunday night
- The UN has labelled the bombings a "monstrous campaign of annihilation"
- It has warned many of the violations may amount to war crimes
As the death toll continues to rise, United Nations human rights chief Zeid Ra'ad al-Hussein labelled the bombing of Ghouta by forces allied to the Syrian Government as a "monstrous campaign of annihilation".
"International humanitarian law was developed precisely to stop this type of situation, where civilians are slaughtered in droves in order to fulfil political or military objectives," he said in a statement.
Information documented by the UN Human Rights office showed at least 346 civilian deaths and 878 injuries, mostly from air strikes on residential areas, since the Syrian Government and its allies escalated an offensive against the rebel-held enclave on February 4.
There were also 15 deaths and 51 injuries reported among civilians in and around Damascus, the result of a dramatic escalation of rebel fire on Government areas.
Many of the violations may amount to war crimes, the UN Human Right chief said.
In New York, UN secretary-general Antonio Guterres appealed for an "immediate suspension of all war activities in Eastern Ghouta".
Speaking to the UN Security Council, Mr Guterres said residents in Ghouta were living in "hell on earth".
He expressed support for a Swedish and Kuwaiti push for the 15-member council to demand a 30-day ceasefire in Syria.
Diplomats said the council could vote on a draft resolution in the coming days.
But Syrian President Bashar al-Assad's veto-wielding ally Russia has called the proposal "not realistic".
Plea for medical supplies
Medical charity Medicines Sans Frontiers (MSF) reported that 13 hospitals and clinics they support have been damaged or destroyed over just the last three days.
MSF made an urgent plea for medical supplies to be allowed into the besieged area.
"We make a plea to those in and around East Ghouta with medical supplies to urgently grant access to those stocks to the medics in East Ghouta — lives depend on it," said Lorena Bilbao, operations coordinator for MSF programmes in Syria.