Bombing waves target rebel-held areas after week-long ceasefire collapses
Rebel-held areas of Aleppo came under heavy bombardment for a second day following an announcement of a major offensive by the Syrian government.
A squadron of five aircraft was in the skies above the city on Friday morning, with bombing waves targeting the east of the city, according to Ammar al Selmo, the head of the civil defence rescue service.
He said the aircraft were Russian and added: "What's happening now is annihilation."
The bombardment is said to have destroyed more than 40 buildings since the operation began on Friday morning, according to Mr al Selmo.
A Syrian military source said the operation was "a comprehensive one" which included a ground offensive, adding that air and artillery attacks could go on "for some time".
It comes only days after a week-long ceasefire collapsed.
Video footage showed burning buildings and a journalist for the AFP news agency described seeing a street on fire after cluster bombs fell.
Incendiary bombs were also among the armaments dropped on the city.
Aleppo is home to 250,000 people and has been under constant government siege since September. Rebels have held the city since 2012.
President Bashar al Assad has denied bombing civilians in the city, and has blamed the West for much of the destruction.
'Long and disappointing' meeting
The US and Russia failed to agree on how to revive the ceasefire following a "long, painful, difficult and disappointing" meeting on Thursday night.
The International Syria Support Group, which includes the US and Russia, met on the sidelines of the UN gathering in New York.
US Secretary of State John Kerry expressed concern at the new Syrian regime offensive in the city.
He said: "We have exchanged ideas with the Russians and we plan to consult tomorrow with respect to those ideas.
"I am no less determined today than I was yesterday but I am even more frustrated."
However, Russian Deputy Foreign Minister Gennady Gatilov has said there will be no new decisions made on Syria on Friday, blaming the position of the United States as the main obstacle to an agreement.
Both countries agreed a deal on 9 September, which included a nationwide ceasefire, improved humanitarian aid access and the possibility of joint military operations against al Qaeda-linked groups.
But it fell apart after the bombing of an aid convoy on Monday, which killed 20 people.
UN Syria mediator Staffan de Mistura said: "The good news is that Russia and the US agreed to work intensely on a possible restoration of it.
"It was a long, painful, difficult and disappointing meeting.
"The next few hours, days maximum are crucial for making it or breaking it."