Russia and the United States faced off at the United Nations over the carnage in Syria on Wednesday, as air strikes pounded Aleppo for a third straight day following the collapse of a ceasefire.
The UN Security Council held crisis talks to try to revive the truce and chart a course towards ending the five-year war in Syria, that has killed 300,000 people.
"We are at a make or break moment," UN Secretary-General Ban Ki-moon told the council, urging world powers to use their influence to help re-start political talks so Syrians can "negotiate a way out of the hell in which they are trapped".
Russia and the United States negotiated the latest ceasefire plan, but Syria ended the truce on Monday following a US-led coalition strike on Syrian soldiers.
Shortly after the truce ended, a UN aid convoy was hit in an air strike that US officials have blamed on Russia.
On Wednesday, heavy bombardment pummelled Aleppo city and the wider province, key battlegrounds in Syria's conflict, and a raid hit a medical team late Tuesday.
Addressing the council, US Secretary of State John Kerry demanded that Russia force Syrian President Bashar al-Assad to ground its air force, blamed for targeting hospitals and barrel-bombing civilians.
"I believe that to restore credibility to the process we must move forward to try to immediately ground all aircraft flying in those key areas in order to de-escalate the situation and to give a chance for humanitarian assistance to flow unimpeded," Kerry said.
Moscow denies that Russian or Syrian planes carried out the strike on Monday on the aid convoy that killed 20 people, and a military spokesman said a coalition drone was in the area when it was destroyed.
Ban told the council he was looking at "options for vigorously investigating" the attack.
- Russia blames rebel groups -
Lavrov told the council that there would be "no more unilateral pauses" by Assad's government forces, arguing that opposition fighters on the ground had used those ceasefires in the past to re-group.
The Russian foreign minister insisted that all sides must rein in rebel groups on the ground to ensure they comply with the ceasefire and said a list of terror groups not covered by the truce should be reviewed.
Only the Islamic State and the Al-Qaeda-linked Nusra Front are not covered by the ceasefire, but Russia, Syria's ally, has long argued that other groups are fighting alongside those jihadists.
"If we can agree on this kind of comprehensive approach, an integrated multi-faced approach, the chances of a cessation of hostilities surviving and being successful will be better," Lavrov said.
The Britain-based Syrian Observatory for Human Rights said dozens of raids hit the city's east overnight, as regime troops advanced on rebels in Aleppo's southwestern outskirts.
At least 11 civilians, including two children, were killed, the highest single-day toll since the truce collapsed this week, said the Observatory.
The Union of Syrian Medical Relief Organisations (UOSSM) said two of its ambulances were hit in Khan Tuman, a village south of Aleppo city, as workers evacuated victims from a previous strike.
Two nurses and two ambulance drivers were killed and another nurse was critically wounded.
- Aleppo under fire -
It was a sleepless night for many Aleppo residents, AFP's correspondent in the city said on Wednesday, with bombardment continuing until rain broke out over the city at dawn.
Civil defense workers in the Qadi Askar neighborhood weaved through rubble in search of wounded residents in a row of buildings hit by air strikes Wednesday.
In the rebel-held neighborhood of Sukkari, Abu Ahmad cleared rubble and shattered glass from his doorstep after bombardment levelled the six-story building next door, killing his neighbors.
He had tea with the 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," Abu Ahmad said.
Syrian state media reported that the city's government-held west had come under rebel shelling, which killed two people.
The United States holds Russia responsible for the attack on the aid convoy, with a US official saying two Russian SU-24 ground attack jets were operating in the area where it was struck.
"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 "unsubstantiated, hasty accusations" seemed designed to "distract attention from the strange 'error' of coalition pilots."
Dozens of Syrian troops were killed in the strike on Saturday by the US-led coalition fighting Islamic State, an attack which Washington said was a mistake.
Russia said the attack endangered a deal reached with Washington that provides for a ceasefire, humanitarian aid deliveries and cooperation between Moscow and Washington in battling IS and other extremist groups.
