Residents speak of "ferocious bombardment" as at least 91 people are killed and nearly two million left without water.
Syrian civilians trapped in the besieged city of Aleppo have made desperate pleas for help, as warplanes pummelled rebel-held areas and deteriorating security conditions left two million people without access to safe drinking water.
Residents of rebel-held eastern Aleppo said "ferocious bombardment" by Syrian and Russian jets on Saturday had levelled neighbourhoods and killed at least 91 civilians.
"We don’t have the equipment to pull the corpses out," a resident said, standing on the rubble of a destroyed building in the city’s al-Bab district.
Describing the horror around him, he said an entire family was killed in a strike, with several people still lying under the debris.
"We are trying to help the injured, those who survived ... but the situation is catastrophic. Destruction and death, everywhere around us. It seems that the Russians and the regime have been given a green light to slaughter us all. As if starving the people here was not enough - it’s now mass murder."
Speaking to Al Jazeera late on Saturday, Abdulkafi al-Hamdo, a professor at the University of Aleppo, said that residents were expecting another night of horror.
"What we are suffering can’t be expressed by words in any language," he said.
"We don’t have water to give our children … [Rescuers] can’t help people anymore and the roads have been cut off by rubble. In the hospitals, there are three-four people on one bed, even in the intensive care units."
Another resident from the al-Mashhad district pleaded with the international community to save the more than 250,000 civilians stuck in besieged areas as air raids continued to flatten civilian areas.
"We urge all honourable people around the world, please, we beg you, come to our aid; save us," he said.
The Syrian military, which is backed by the Russian air force, said on Monday it was starting a new offensive to recapture opposition-controlled areas in Aleppo, ending a week-long US-Russia brokered ceasefire following a US-led coalition air strike on a Syrian army post.
Since then, at least 180 people have been killed in rebel-held areas of Aleppo province, including the besieged eastern part of the city, the Syrian Observatory for Human Rights said on Saturday.
The residents’ pleas came as the UN said nearly two million people in Aleppo were without running water amid worsening humanitarian and security conditions.
Hanaa Singer, a UNICEF representative in Syria, said intense air attacks damaged the Bab al-Nairab station that supplies residents in rebel-held eastern parts with water.
Singer said rebels shut down the Suleiman al-Halabi pumping station in retaliation, cutting water to 1.5 million people in government-held western parts of the city.
"Depriving children of water puts them at risk of catastrophic outbreaks of water-borne diseases," Singer said in a statement released late on Friday.
Meanwhile, Syrian rebels said late on Saturday they had regained control of Handarat, a former Palestinian refugee camp north of Aleppo city, after it had earlier fallen to government soldiers.
Rami Abdulrahman, the director for the Syrian Observatory for Human Rights said the fighting was "back and forth" and inconclusive.
An army statement had earlier said that Handarat, an elevated ground overlooking one of the main roads into Aleppo, had been captured and that a "large numbers of terrorists" had been killed.
The army’s assault on Handarat marks the first major ground advance by the government in an offensive that rebels say has unleashed unprecedented firepower against their half of the city.
Residents in the rebel-held zones say there is no safe way for them to flee the besieged area.
International efforts to enforce a ceasefire have failed and there appears to be no ongoing political track that will bring about any immediate cessation of hostilities.
Moreover, many besieged areas, with hundreds of thousands of people, remain without aid.
Humanitarian deliveries have been further hampered by an attack on Monday on an aid convoy outside Aleppo, which killed 20 people. The US blames Russia for the attack, but Moscow has rejected the allegation.
While 36 trucks from the international Red Cross entered al-Waer, in the central city of Homs, Jens Laerke, spokesman for the Office for the Coordination of Humanitarian Affairs, has previously said that aid convoys will not go to Aleppo .
The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly escalated into a full-blown armed conflict.
Five years on, more than 400,000 Syrians are estimated to have been killed, and almost 11 million Syrians - half the country’s prewar population - have been displaced from their homes.