New air strikes on the Syrian rebel enclave of Eastern Ghouta on Saturday took the civilian death toll from seven days of devastating bombardment to more than 500 after the United Nations again delayed a vote on a ceasefire.
More than 120 children have been among the dead in the bombing campaign that the regime launched last Sunday on the enclave just outside Damascus, the Syrian Observatory for Human Rights said.
The Britain-based monitor of the war said at least 29 civilians were killed in Saturday's strikes, including 17 in the main town of Douma.
It has said the strikes are being carried out by Syrian and Russian forces. Moscow, which intervened militarily in support of its Damascus ally in 2015, has denied any direct involvement in the Eastern Ghouta bombardment.
US President Donald Trump on Friday said Russia's recent actions in Syria were a "disgrace".
The UN Security Council had been due to hold a vote on Friday on a resolution calling for a month-long ceasefire to allow aid deliveries and the evacuation of seriously wounded civilians.
But the vote was postponed until 1700 GMT on Saturday as Western powers bickered with Russia over the wording.
- Rebel fire on Damascus -
Control of Eastern Ghouta is shared between two Islamist factions and Syria's former Al-Qaeda affiliate, and Russia insists there can be no ceasefire with the jihadists or their allies.
Russia has been pressing for a negotiated withdrawal of rebel fighters and their families like the one that saw the government retake full control of second city Aleppo in December 2016.
But all three rebel groups have refused.
World leaders have expressed outrage at the plight of civilians in Eastern Ghouta, which UN chief Antonio Guterres called "hell on earth", but have so far been powerless to halt the bloodshed.
The enclave is completely surrounded by government-controlled territory and its 400,000 residents are unwilling or unable to flee the deadly siege.
The rebels have been firing back into Damascus, where a hospital was hit on Friday, state news agency SANA reported.
At least 16 civilians have been killed in eastern districts of the capital since Sunday, according to state media, and many residents have sought temporary accommodation elsewhere for fear of a further intensification of the fighting.
- 'Unbelievable' -
At the United Nations, US ambassador Nikki Haley expressed dismay as negotiations dragged on to secure Russian approval for a ceasefire resolution.
"Unbelievable that Russia is stalling a vote on a ceasefire allowing humanitarian access in Syria," Haley posted on Twitter.
"How many more people will die before the Security Council agrees to take up this vote? Let's do this tonight. The Syrian people can't wait."
Russia has vetoed 11 draft resolutions on Syria to block action that targeted its ally. In November, it used its veto to end a UN-led investigation of chemical weapons attacks in Syria.
German Chancellor Angela Merkel and French President Emmanuel Macron wrote to Russian counterpart Vladimir Putin on Friday to ask him to back the ceasefire.
Negotiations have stumbled over a key provision of the draft resolution that specifies when the ceasefire will begin.
Following hours of tough negotiations, an amended draft was circulated that demands a 30-day ceasefire "without delay," while stopping short of specifying the timing.
A previous draft had said the ceasefire would go into force 72 hours after the adoption, but that was dropped from the text in a bid to reach compromise with Russia.
In another concession to Russia, the draft also specifies that the ceasefire will not apply to operations against the Islamic State group or Al-Qaeda, along with "individuals, groups, undertakings and entities associated" with the blacklisted terror groups.
The text would demand the immediate lifting of all sieges, including that on Eastern Ghouta, and order all sides to "cease depriving civilians of food and medicine indispensable to their survival".