Russia has said there is no agreement on a UN Security Council resolution to bring in a 30-day truce in Syria.
Russia's UN ambassador, Vassily Nebenzia, told the council in New York his country had presented amendments.
Speaking at an emergency meeting of the council, he called for "feasible" rather than "populist" action.
Calls for a truce have grown louder as civilians in the besieged rebel enclave of the Eastern Ghouta come under more intensive bombardment.
What does the resolution say?
The draft, put forward by Kuwait and Sweden, calls for a 30-day nationwide truce to go into effect 72 hours after adoption.
Medical evacuations and aid deliveries would start 48 hours after that.
But any ceasefire would not apply to the Islamic State group, al-Qaeda and the al-Nusra Front.
Russian Foreign Minister Sergei Lavrov has made clear that Hayat Tahrir al-Sham, an al-Qaeda-linked alliance that has a presence in the Eastern Ghouta, must not be included.
Mr Lavrov said he also wanted to exclude rebel groups in the enclave who are "co-operating" with Hayat Tahrir al-Sham and shelling nearby government-held areas.
The United States, the UK and France are calling for the resolution to be approved without delay.
What are the Russian Objectives?
Russia's UN ambassador, whose country is one of the five powers that can veto a resolution, stressed the need for something that would actually work.
"The ceasefire carries great significance in principle and not merely for the delivery of humanitarian assistance," he said.
"The challenge is how to achieve this. And here what we need is not symbolism, not decisions for the sake of decisions, but rather measures that are undertaken that are commensurate with conditions on the ground."
Russia is a key backer of Syria's President Basher al-Assad in the civil war and the suspicion among Western powers is that Moscow is stalling to allow their ally to deal a final blow to rebel forces.
Deputy US ambassador to the UN Kelley Currie accused Russia of standing in the way of "any meaningful effort" to halt the fighting in the Eastern Ghouta.
how bad is the situation in Eastern Ghouta?
For the fifth day running, Syrian government forces carried out a wave of air and artillery strikes.
The number killed since Sunday has risen to at least 403, the Syrian Observatory for Human Rights monitoring group says, as 46 more died on Thursday.
Barrel bombs and shell fire have rained down in what the UN has described as "hell on earth" for the 393,000 people trapped there.
The Syria Civil Defence, whose rescue workers are widely known as the White Helmets, said residential areas in the town of Douma came under sustained attack, first from ground-to-ground rockets and then government and Russian jets.
Spokesman Siraj Mahmoud also asserted that the organisation was being deliberately targeted by government aircraft, with four rescuers killed since Sunday night.
"Everyone knows it is an extermination," he told the Associated Press.
The Syrian state news agency meanwhile reported that a child was killed and six civilians wounded in the government-controlled Barzeh district of Damascus by rebel shellfire. Army units responded with "precision strikes", destroying a number of rebel positions and inflicting heavy losses, it said.
The UN humanitarian co-ordinator for Syria, Panos Moumtzis, echoed calls for a ceasefire.
Referring to the harrowing images coming out of the Eastern Ghouta, he said: "If this is not going to convince [UN security] council members, council states, of the need for a ceasefire, honestly we don't know what is it that would convince them."
The Syrian government has denied targeting civilians and insisted it is trying to liberate the Eastern Ghouta from "terrorists" - a term it has used to describe both jihadist militants and the mainstream rebel groups that dominate the enclave.
Aid groups report dozens of hospitals being put out of action since Sunday.
Médecins Sans Frontières (MSF) said the government's siege was also preventing medics from obtaining essential life-saving supplies, warning that its facilities had completely run out of supplies of blood bags, general anaesthetic drugs and intravenous antibiotics.
Separately, Iran's Deputy Foreign Minister, Abbas Araghchi, has told the BBC "fear of war is everywhere in our region" and at the same time described the situation with Iran's Syrian ally as "very complicated".
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