Aleppo (Syria) (AFP) - Air raids and shelling pounded key battlefronts in Syria on Tuesday, as outrage mounted over a strike on an aid convoy hours after Syria's military declared an end to a week-long truce.
The raid and renewed violence across the country dimmed hopes that the fraught ceasefire negotiated by Moscow and Washington could be revived.
Key players including the United States and Russia were to meet in New York Tuesday in an effort to salvage the peace process, which US Secretary of State John Kerry had warned could be the "last chance" to end Syria's civil war.
But on the ground in Syria, activists and AFP correspondents reported intensifying fighting.
In the battleground city of Aleppo, air raids and artillery fire hit rebel-held districts until approximately 2:00 am (2300 GMT Monday), an AFP correspondent said.
Residents spent the night huddled in their apartments sharing news about the collapsing truce via text messages and heard loud intermittent booms on Tuesday morning.
At least 39 civilians were killed in overnight bombardment of Aleppo and the surrounding province, the Syrian Observatory for Human Rights monitoring group said, and fresh clashes had erupted on the southern edges of the city.
In the week after the truce was declared on September 12, only 27 civilians were killed as fighting dropped significantly across the country.
Those killed overnight included 12 people, mostly humanitarian workers, who died on a raid on a joint United Nations, Red Cross, and Red Crescent convoy delivering assistance to the town of Orum al-Kubra in Aleppo province.
- UN 'war crime' warning -
An infuriated United Nations warned Monday night's attack, which destroyed at least 18 trucks in the 31-vehicle convoy, could amount to a war crime.
"Let me be clear: if this callous attack is found to be a deliberate targeting of humanitarians, it would amount to a war crime," aid chief Stephen O'Brien said.
"Our outrage at this attack is enormous," the UN envoy for Syria, Staffan de Mistura, told reporters.
"The convoy was the outcome of a long process of permission and preparations to assist isolated civilians."
An AFP correspondent at the scene of the strike early Tuesday saw damaged boxes of medical supplies and bags of aid spilling out of charred green trucks.
Aid deliveries to desperate civilians were a key element of the US-Russia deal.
But there were only three known aid delivery operations during the week-long truce: to Moadamiyet al-Sham near Damascus on Sunday and to both Talbisseh and Orum al-Kubra on Monday.
Cross-border aid for besieged civilians in eastern parts of Aleppo city never entered Syrian territory.
Syria's military unilaterally announced the end to the truce on Monday night, accusing rebels of more than 300 violations and failing to "commit to a single element" of the deal.
In the northwestern province of Idlib on Tuesday, activist Nayef Mustafa said planes circled over the town of Salqin, held by Syria's former Al-Qaeda affiliate in alliance with Islamist rebels.
- 'Ready for barrel bombs' -
"It's calm now, but there was machinegun fire by military aircraft overnight," Mustafa told AFP.
"The ceasefire has collapsed and people are getting ready to be hit by barrel bombs."
At least four air strikes hit the central rebel-held town of Talbisseh Tuesday morning after artillery fire throughout the night, activist Hassaan Abu Nuh said.
The truce deal's primary sponsors, Washington and Moscow, and other key players in the International Syria Support Group will meet in New York on Tuesday to assess the situation.
Kerry will try to speak to Russian Foreign Minister Sergei Lavrov in New York, where leaders are gathered for the UN General Assembly, before Tuesday's meeting.
The two top diplomats had negotiated the deal in Geneva earlier this month, hoping to put an end to more than five years of conflict in which more than 300,000 people have been killed.
The UN Security Council will also hold a session on Syria on Wednesday, but statements from Syrian and Russian military officials appeared to bury hopes of reviving the truce deal.
"Considering that the conditions of the ceasefire are not being respected by the rebels, we consider it pointless for the Syrian government forces to respect it unilaterally," said Russian Lieutenant General Sergei Rudskoy.
The truce had already come under massive strain when a US-led coalition strike on Saturday hit a Syrian army post near the eastern city of Deir Ezzor, where government forces are battling the Islamic State jihadist group
Syrian President Bashar al-Assad on Monday blasted the strike, which killed dozens of troops, as "flagrant American aggression".