Rescue workers in Aleppo struggled to help hundreds of wounded Syrians trapped in a massive Russian-backed regime air offensive as the bloody battle to recapture the key city entered its fifth day.

Dozens of air strikes hit opposition-held areas of the northern Syrian city on Monday with the UK-based Syrian Observatory for Human Rights saying at least 12 people, including three children, were killed.

More than 280 people have died in the city's opposition-held east since the offensive began on Thursday after a ceasefire ended with at least 400 people wounded - including 61 children - on Sunday alone, a doctors' group said.

The Syrian regime offensive to recapture all of Aleppo - with Russian air support and Iranian help on the ground - has been accompanied by bombing that residents describe as unprecedented in its ferocity.

Only 30 doctors now remain in Aleppo's east, where residents are in dire need of medical and surgical supplies to treat the wounded among a trapped population of 300,000.

"There are 30 doctors who are still inside the eastern Aleppo city," Abd Arrahman Alomar, a pediatrician who works for the Syrian American Medical Society (SAMS) in opposition-controlled areas, told a news briefing in Geneva.

They lack equipment and emergency medicine to treat the many trauma cases, and there is only enough fuel to run hospital generators for 20 days. One obstetrician and two pediatricians remain to care for pregnant women and 85,000 children, he said.

"The sudden rise in wounded now means supplies are dangerously low or not available at all," said Al Jazeera's Charles Stratford, reporting from Gaziantep along the Turkey-Syria border.

"Medics say they can't transport people to other hospitals in safe areas because eastern Aleppo is surrounded by regime forces."

Dr Alomar said if the bombing continues, "we are going to the point of zero where there are no facilities to be protected, where there is no health staff to be protected".

Diplomacy 'not dead'

Moscow and Damascus launched their assault last week despite months of negotiations led by US Secretary of State John Kerry that resulted in a short-lived ceasefire this month.
Kerry said the failed truce was not the cause of the fighting, and that diplomacy was the only way to stop the war.

"The cause of what is happening is Assad and Russia wanting to pursue a military victory," Kerry told reporters during a trip to Colombia.

"Today there is no ceasefire and we're not talking to them right now. And what's happening? The place is being utterly destroyed. That's not delusional. That's a fact."

On Monday, dozens of opposition and their families quit the last opposition-held district of central Homs city, as part of a deal struck with the regime last year.

A total of 131 fighters and 119 family members were bussed out of Waer, devastated after a three-year regime siege, to opposition-held Dar al-Kubra further north, according to Reuters news agency.

An estimated 600,000 Syrians live under siege, according to the UN, with most encircled by regime forces.

The UN's World Food Programme said it delivered food aid on Sunday to civilians in four besieged towns in Syria for the first time since April.

A convoy of 53 trucks entered Madaya and Zabadani, with another 18 to Fuaa and Kafraya, according to the International Committee for the Red Cross.

At an emergency UN Security Council council meeting on Sunday, US envoy Samantha Power voiced some of the strongest criticism yet of Russia's support for President Bashar al-Assad's regime.

"What Russia is sponsoring and doing is not counter-terrorism. It is barbarism," she said. The UK's envoy accused Moscow of committing war crimes.

The Kremlin hit back on Monday with Russian spokesman Dmitry Peskov denouncing "the overall unacceptable tone and rhetoric of the representatives of the United Kingdom and the United States, which can damage and harm our relations".

UN Secretary General Ban Ki-moon called on world powers to "work harder for an end to the nightmare" in Syria, which has killed an estimated 400,000 people and driven millions from their homes.

PHOTO CAPTION

A man walks on the rubble of damaged buildings after an airstrike on the opposition held al-Qaterji neighborhood of Aleppo, Syria September 25, 2016. REUTERS

Al-Jazeera