As the death toll in Syria's Eastern Ghouta surpasses 470, a UN Security Council vote on a draft resolution seeking a 30-day ceasefire across the country is under way.

The vote has already been delayed several times, after council members tried to convince Russia to agree to a resolution.

More than 500 people, including 123 children, have been killed in the Damascus suburb since Sunday, according to UK-based The Syrian Observatory for Human Rights (SOHR).

Another 2,400 people have been wounded, SOHR said on Saturday. Dozens of other people were missing "under the rubble", it added, as Russian-backed Syrian forces continued their aerial assault on the rebel-held enclave, home to some 400,000 people.

Eastern Ghouta is the last remaining rebel-held area east of Damascus and has been under siege by Syrian President Bashar al-Assad's forces since 2013.

The draft UNSC resolution, sponsored by Kuwait and Sweden, is aimed at implementing a ceasefire to allow aid delivery and the evacuation of civilians from the besieged suburb.

Al Jazeera's Diplomatic Editor James Bays, reporting from the UN headquarters in New York, said on Friday that the ongoing delay was due to a disagreement between Russia and other Security Council members over the latest version of the resolution.

"There were certainly changes made [to the resolution] on Thursday after the Security Council meeting," he said.

"They [Security Council members] changed some of the language."

The UN special envoy for Syria, Steffan de Mistura, stressed the urgent need for a ceasefire to stop the "horrific heavy bombardment of Eastern Ghouta and the indiscriminate mortar shelling on Damascus".

Russian UN ambassador Vassily Nebenzya had said there was "no agreement" and presented amendments to the draft resolution "for it to be realistic", while the Syrian ambassador to the UN, Basher al-Jaafari, accused the international body and mainstream media of backing "terrorists recruited by the US from all over the world" to fight in Syria.

In response, Nikki Hailey, the US ambassador to the UN, called Russia's actions as "unbelievable" on Twitter.

Unbelievable that Russia is stalling a vote on a ceasefire allowing humanitarian access in Syria. How many more people will die before the The Security Council agrees to take up this vote? Let’s do this tonight. The Syrian people can’t wait. — Nikki Haley (@nikkihaley) February 23, 2018

The "relentless" shelling, coupled with live artillery fire, has exacerbated an already dire humanitarian situation amid the ongoing siege.

The blockade has prevented basic necessities, such as food and medicine, from entering the enclave. The siege has also resulted in huge inflation of the cost of basic goods. A bag of bread now costs the equivalent of $5.

In addition, malnutrition rates have reached unprecedented levels, according to the UN Office for the Coordination of Humanitarian Affairs.

Earlier this week, the UN and other international bodies expressed outrage at the number of civilian casualties. The UN called for an "immediate" stop to the "escalation" of violence.

Hundreds of thousands of people have died in fighting during Syria's seven-year civil war, and millions have been forced to flee the country.