Syria claims new offensive, diplomats fail to renew truce

It was a long, painful, difficult and disappointing meeting, said the UN special envoy for Syria

Syria announced a new offensive against rebel-held areas of Aleppo on Thursday while diplomats failed to find a way in New York to revive a US and Russian-brokered ceasefire that collapsed this week.

Warplanes mounted the heaviest air strikes in months against rebel-held districts of Syria's commercial hub and largest city, dealing a fresh blow to efforts to end Syrian civil war that has raged since 2011.

Hamza al-Khatib, the director of a hospital in the rebel-held east, told Reuters 45 people were killed.

"It's as if the planes are trying to compensate for all the days they didn't drop bombs" during the ceasefire, Ammar al-Selmo, the head of the civil defence rescue service in opposition-held eastern Aleppo, told Reuters.

Syrian state media announced the new offensive and quoted the army's military headquarters in Aleppo urging civilians in eastern parts of the city to avoid areas where "terrorists" were located and said it had prepared exit points for those who want to flee, including rebels.

Syrian President Bashar al-Assad indicated he saw no quick end to the war, telling the Associated Press it would "drag on" as long as it is part of a global conflict in which terrorists are backed by Saudi Arabia, Qatar, Turkey and the United States.

On Saturday, the US-led coalition against the Islamic State militant group carried out a lethal air raid on Syrian government troops.

On Monday, the ceasefire foundered further with an attack on an aid convoy that killed around 20 people and that Washington blamed on Russian planes. Russia denied involvement.

Foreign ministers emerged from a meeting in New York having failed to find a way back to a ceasefire, though US Secretary of State John Kerry said he was willing to keep trying if Russia came back with new ideas.

"I am no less determined today than I was yesterday but I am even more frustrated," Kerry told reporters after the session.

"It was a long, painful, difficult and disappointing meeting," the UN Syria envoy Staffan de Mistura told reporters after the meeting of the International Syria Support Group.