Air strikes continue to hammer the city of Aleppo as world powers with a stake in Syria's civil war are meeting in New York.
The United States and Russia on Thursday are chairing a meeting that will bring together the 23-nation International Syria Support Group (ISSG), set up to push for a ceasefire and an eventual political resolution to the five-year-old conflict.
Diplomats told AFP news agency that it would take place at 2pm (18:00 GMT) in a New York hotel.
The meeting comes amid accusations between the ISSG co-chairs, John Kerry, the US secretary of state, and the Russian Foreign Minister Sergey Lavrov.
The US blames Russia for carrying out a deadly air strike on a UN aid convoy on Monday in northern Syria after Syrian President Bashar al-Assad's military declared the ceasefire over.
Russia denies any role in the attack and in turn accuses Washington of failing to ensure that the US-backed opposition forces fighting Assad respected the truce.
After halting aid operations in response to the convoy attack, the UN on Thursday said it was ready to resume humanitarian deliveries.
Since the collapse of the truce, dozens of raids hit eastern Aleppo as government troops advanced on rebels in the city's southwestern outskirts, according to the Britain-based Syrian Observatory for Human Rights.
At least 12 civilians, including two children, were killed, the highest single-day toll since the truce collapsed this week, the monitor said.
In northwest Idlib province, 18 Syrians were killed during bombings on the town of Khan Sheikhun, according to the group.
In the village of Khan Tuman, south of Aleppo city, two nurses and two drivers were killed in an attack on two ambulances, the Union of Syrian Medical Relief Organisations said.
Syrian state media reported that the city's government-held west had come under rebel shelling, which killed two people.
'Hanging by a thread'
Despite the differences between Kerry and Lavrov, both agree that the US-Russian effort is the only way available to impose a ceasefire.
Kerry has demanded that Russia order Assad to ground his air force in order to re-establish the credibility of the peace effort in the eyes of the suspicious opposition.
Lavrov has countered that the UN Security Council should consider adding some more of the anti-Assad rebel groups to its list of proscribed "terrorist" organisations.
Asked whether the ceasefire could be salvaged, Kerry said that he would meet Lavrov once again to try to narrow their differences.
But he added: "It's going to be very difficult. We'll see what people are willing to do."
If either side is able to come up with concrete measures to restore the truce, they could be endorsed by the ISSG at the meeting and the peace process would continue.
Failing that, Kerry has admitted that Syria's future is "hanging by a thread".
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