Warplanes launched some of the heaviest air strikes yet on rebel-held areas of Aleppo on Friday after the Russian-backed Syrian army declared an offensive to fully capture Syria's biggest city, killing off any hope of reviving a ceasefire.
Residents said the streets were deserted as the 250,000 people still trapped in the besieged opposition-held sector of Aleppo sought shelter from jets.
The rebels and the Syrian Observatory for Human Rights monitoring body described raids by sophisticated jets they said must belong to Russia. Residents also spoke of attacks by helicopters using bombs made from oil drums, a tactic usually attributed to the Syrian army.
"Can you hear it? The neighbourhood is getting hit right now by missiles. We can hear the planes right now," Mohammad Abu Rajab, a radiologist, told Reuters.
"The planes are not leaving the sky, helicopters, barrel bombs, warplanes."
The intensive bombardment left no doubt that the Syrian government and its Russian allies had spurned a plea from US Secretary of State John Kerry to halt flights to resurrect the ceasefire, which lasted a week before collapsing on Monday.
Casualties are evacuated after Syrian regime airstrikes hit Aleppo's opposition controlled Al-Ansari town, Syria Source: Getty Images
A rebel commander said the blasts were the fiercest the city had faced.
"I woke up to a powerful earthquake though I was in a place far away from where the missile landed," he said.
In a late night announcement on Thursday, the Syrian military announced "the start of its operations in the eastern districts of Aleppo", and warned people to stay away from "the headquarters and positions of the armed terrorist gangs".
The statement gave no details of what the operation may entail - eastern Aleppo had already been the target of intense air strikes on Thursday. A source close to Damascus told Reuters on Friday a major ground operation had yet to begin.
"Military operations include everything, and of course the most important part is the ground operation," the source said.
There was no immediate comment from the Russian or Syrian militaries on Friday's air strikes.
Syrian boys dive into a hole filled with water that was caused by a missile attack in the rebel-held neighborhood of Sheikh Saeed in Aleppo Source: AAP
The Syrian army's declaration of the offensive coincided with international meetings on Syria in New York, the latest diplomatic efforts officially intended to revive the truce, which was brokered by the United States and Russia.
Its collapse, the same fate as all previous efforts to halt a 5-1/2-year-old war that has killed hundreds of thousands of Syrians, has doomed what may be the final bid for a peace breakthrough before President Barack Obama leaves office.
