The UN Security Council yesterday delayed a vote on a demand for a 30-day ceasefire in Syria, where pro-government warplanes have been pounding the last rebel bastion near Damascus in one of the deadliest bombing campaigns of the seven-year civil war.

A draft resolution aimed at ending the carnage in the eastern Ghouta district and elsewhere in Syria will be put up for a vote in the 15-member council at noon (1700 GMT) today, Kuwait's UN Ambassador Mansour Ayyad Al-Otaibi said.

The 24-hour delay followed a flurry of last-minute negotiations on the text drafted by Sweden and Kuwait after Russia, a veto-holding ally of Syrian President Bashar al-Assad, proposed new amendments on Friday.

'Unbelievable that Russia is stalling a vote on a ceasefire allowing humanitarian access in Syria,' US Ambassador to the UN Nikki Haley posted on Twitter.

Talks have centred on the paragraph demanding a cessation of hostilities for 30 days to allow aid access and medical evacuations. A proposal for the truce to start 72 hours after the resolution's adoption has been watered-down to instead demand it start 'without delay' in a bid to win Russian support.

Diplomats, speaking on condition of anonymity, said Moscow does not want to specify when a truce should start. It was not immediately clear how Russia would vote on Saturday. A resolution needs nine votes in favour and no vetoes by Russia, China, the United States, Britain and France to be adopted.

'We're not going to give up ... I hope that we will adopt something forceful, meaningful, impactful tomorrow,' Olof Skoog, Sweden's UN ambassador, told reporters.

Previous ceasefires, however, have had a poor record of ending fighting in Syria, where Assad's forces have gained the upper hand.

The towns and farms of eastern Ghouta have been under government siege since 2013, with shortages of food, water and electricity that worsened last year. Earlier on Friday, the densely populated enclave was bombed for a sixth straight day, witnesses said.

The civilian casualties and devastation there are among the worst in Syria since the government captured rebel-held parts of Aleppo in 2016. At least 462 people have been killed, including at least 99 children, and many hundreds injured, the Syrian Observatory for Human Rights monitoring group said on Friday.

Syrian state media reported one person was killed and 58 injured in rebel shelling of sites in Damascus, including a hospital.

Clouding any potential ceasefire is the Syrian government's frequently used tactic of pushing rebels to surrender their strongholds after long sieges and military offensives.

Insurgents in eastern Ghouta have vowed not to accept such a fate, ruling out an evacuation of fighters, their families and other civilians of the kind that ended rebellions in Aleppo and Homs after heavy bombardment in earlier years.

'We refuse categorically any initiative that includes getting the residents out of their homes and moving them elsewhere,' Ghouta rebel factions wrote in a letter to the Security Council.

Eastern Ghouta has 400,000 people spread over a larger area than other enclaves the government has recaptured. Late on Thursday, government aircraft dropped leaflets urging civilians to depart and hand themselves over to the Syrian army, marking corridors through which they could leave safely.