End this hell, UN chief tells world powers at crucial Syria talks

World powers were told they face a "make or break moment" in Syria, as the UN Security Council held a crisis meeting and violence flared after the failure of a seven-day ceasefire.

UN Secretary-General Ban Ki-moon on Wednesday told the New York meeting that members must use their influence "to negotiate a way out of the hell" in which Syrians are trapped, after two disastrous days since the end of the US-Russia brokered truce.

Russia and the US remain locked in confrontation over the bombing of a UN aid convoy in Aleppo on Monday evening that killed 20 people - an attack the US on Wednesday blamed directly on Russian forces. Russia denies any role.

John Kerry, the US secretary of state, told the meeting he believed there was a way out "of the carnage" and called for the grounding of the Syrian and Russian air forces.

The UN said late on Wednesday that it would resume aid deliveries that were suspended after the air strike. 

"The preparation for these convoys has now resumed and we are ready to deliver aid to besieged and hard-to-reach areas as soon as possible," the UN Office for the Coordination of Humanitarian Affairs said in a statement.

Meanwhile in Moscow, Russia's defence minister announced he was dispatching his navy's flagship aircraft carrier to bolster forces off the coast of Syria.

"Currently the Russian naval deployment to the east Mediterranean consists of no less than six battleships and three or four support vessels," Sergei Shoigu said.

"In order to bolster the military capabilities of the group we plan to add the Admiral Kuznetsov aircraft carrier to the group."

The announcement coincided with the Security Council meeting.

There were also reports of dozens being killed in intense bombing of Aleppo on Wednesday, including four medical workers in an attack that destroyed two ambulances in Khan Tuman, a village south of the city.

The Union of Syrian Medical Relief Organisations said two nurses and two ambulance drivers were hit as they moved victims from a previous attack.

The British-based activist group, the Syrian Observatory for Human Rights, said dozens of raids hit Aleppo's eastern area overnight, as government troops advanced on the city's southwestern outskirts.

Civil defence workers in the Qadi Askar area weaved through rubble in search of wounded residents in a row of buildings hit by air strikes. 

In the rebel-held area of Sukkari, Abu Ahmad cleared rubble and shattered glass from his doorstep after bombardment levelled the six-storey building next door, killing his neighbours.

He had had tea with two brothers who lived in the building late the previous night. 

"Just an hour after I left, a missile destroyed their whole building and they both died under the rubble," Ahmad said.  

Syrian state media reported that the city's government-held west had come under rebel shelling, which killed two people.

Seven civilians, including three children, were also killed in unidentified air raids on the northwestern town of Khan Sheikhun on Wednesday, according to the observatory.

Bombardment has escalated across the country since Monday evening, when Syria's military declared an end to the week-long truce that had brought relative calm to major fronts. 

Hours after the announcement, the air strike hit the UN aid convoy near Aleppo, killing 20 and destroying 18 trucks, the Red Cross said. 

Monday's strike sparked international outrage and prompted an exasperated UN to suspend all humanitarian convoys across Syria.

"There only could have been two entities responsible, either the Syrian regime or the Russian government," President Barack Obama's national security spokesman Ben Rhodes said.

"In any event, we hold the Russian government responsible for air strikes in this space."

On Wednesday, Moscow claimed a US drone was flying in the area at the time of the attack.

'Hasty accusations'

Two Russian SU-24 ground attack jets were operating in the area where the aid convoy was struck, another US official told AFP. 

"The best evaluation we have is that the Russians carried out the strike," he added, speaking on condition of anonymity.

The Russian foreign ministry said the comments were "Unsubstantiated, hasty accusations" designed to "distract attention from the strange 'error' of coalition pilots".

This was a reference to Saturday's bombardment and killing of at least 62 Syrian troops by the US-led coalition fighting the Islamic State group, an attack that Washington said was a mistake.

Despite the tensions, Kerry insisted that efforts to salvage the truce were "not dead", after a short meeting of the 23-nation International Syria Support Group in New York, where world leaders have gathered for the UN General Assembly. 

Kerry's spokesman John Kirby said it had been agreed that "despite continued violence", diplomats would use the agreement between the US and Russia as a basis for more talks.

The deal foresaw an end to fighting between President Bashar al-Assad's forces and 'moderate' rebels, aid deliveries to besieged areas and, if the ceasefire held for seven days, cooperation between Moscow and Washington in battling IS and other extremist groups.