Rebel-held eastern Aleppo was hit by dozens of airstrikes Friday, hitting emergency service structures and damaging underground shelters, residents said.
At least 93 people were killed in the strikes in Aleppo province on the second consecutive day of fierce attacks, according to the White Helmets rescue group.
Ibrahim al-Hajj, a volunteer with the group, said residents of the rebel-held side, which is under siege, could not flee and people were largely cowering inside their homes.
The Syrian government had promised in a statement Thursday to allow residents of eastern districts to escape to government-held western districts. The UN estimates there are some 250,000 people in the rebel-held areas.
"Nothing about what the regime said about corridors is real, nothing. How can we move on the streets if we don't feel safe? If it was real I would leave now," said Mustafa, a 48-year-old man who lives with his two elderly parents, his wife and daughter.
"They want a road to leave Aleppo," says al-Hajj. "People are waiting on God's mercy."
The airstrikes include the use of incendiary bombs and cluster munitions, according to residents, who blame forces loyal to President Bashar al-Assad and Russia, the main backer of the government, for the aerial attacks.
"We feel the earth trembling and shaking under our feet. Aleppo is burning," activist Bahaa al Halabi told dpa from the besieged rebel-held districts.
"People are not safe anymore, even in shelters," resident Yassin Abu Raed said. Other residents also said the latest raids were destroying underground shelters people had built.
Water stations have been badly damaged and humanitarian aid has not reached the rebel-held district in many weeks. One resident said people were eating mostly stockpiled rice and lentils.
UNICEF in a statement late Friday said nearly 2 million people in Aleppo are now once again with no running water through the public network.
“Intense attacks last night have damaged the Bab al-Nayrab water pumping station which supplies water to some 250,000 people in the eastern parts of Aleppo. Violence is preventing repair teams from reaching the station," said the statement.
In retaliation, rebels switched off the Suleiman al Halabi pumping station, also located in the east, cutting off water to 1.5 million people in the regime-held western parts of the city, it added.
Aleppo, Syria's pre-war commercial hub, has been divided between government forces in the west and rebels to the east since fighting erupted for the control of the city in mid-2012.
“Depriving children of water puts them at risk of catastrophic outbreaks of waterborne diseases and adds to the suffering, fear and horror that children in Aleppo live through every day," the UNICEF statement said.
The UN agency expressed concen that in the eastern part of Aleppo, the population will have to resort to highly contaminated well water, while in the western part existing deep ground water wells will provide a safe alternative water source for the time being.
The Syrian military announced late on Thursday it was launching a ground invasion of the eastern districts, though the actual offensive appeared to have been somewhat delayed.
The army has called on residents of the east to move to government-held western districts.
"Shell us, starve us ... no matter what you do, we are staying here," activists in eastern Aleppo posted on Facebook pages in response.
US Secretary of State John Kerry has said he is determined to restore a failed ceasefire brokered with Russia, calling on the Syrian regime and Moscow to "do their part" to ease the suffering of the Syrian people.
Kerry and his Russian counterpart Sergei Lavrov spoke informally Friday about the next step in the conflict in New York, a senior State Department official told dpa, describing the discussion as constructive.
Lavrov later told the UN General Assembly it was "high time to learn lessons and prevent a slide down to catastrophe in Syria" and called on the US and it's allies to begin separating moderate opposition groups from terrorists - namely the Jabhat Fatah al-Sham, a former al-Qaeda-linked group previously known as the al-Nusra Front.
There was no point to having a truce without the separation of extremists, Lavrov told reporters. He called on the US to begin engaging with Russian military experts on creating a map of Syria outlining areas held by extremists.
On Monday, a UN aid convoy was attacked in what the US says was a Russian airstrike, though Moscow rejects the charges, despite growing evidence to back Washington's case. At least 21 people were killed and 18 trucks destroyed. Only one other convoy has passed since then.