Residents in Syria's battleground city of Aleppo cowered indoors Saturday as fierce air strikes toppled buildings and killed at least 45 civilians, after diplomatic efforts to revive a ceasefire failed.
Nearly two million civilians were left without water in the devastated northern city after regime bombardment damaged a pumping station and rebels shut down another in retaliation, the United Nations said.
UN chief Ban Ki-moon said he was "appalled by the chilling military escalation" since the Syrian army on Thursday announced the launch of an offensive backed by Russian air raids to oust rebels from eastern Aleppo that has cost around 100 lives.
The use of bunker buster bombs and other advanced munitions against civilians may amount to war crimes, he warned.
Voicing indignation, US Secretary of State John Kerry who failed in talks this week with Russian counterpart Sergei Lavrov to revive a ceasefire said: "What is happening in Aleppo today is unacceptable. It is beyond the pale."
"If people are serious about wanting a peaceful outcome... they should cease and desist bombing innocent women and children, cease cutting off water and laying siege in mediaeval terms to an entire community," he said.
Kerry had harsh words for Moscow's involvement in the conflict, in comments at a meeting with his European counterparts.
"Russia needs to set an example, not a precedent -– an unacceptable precedent, I might add, for the entire world," he said.
Syria's Foreign Minister Walid Muallem, for his part, told the UN General Assembly that the army and its allies were making "great strides" in the conflict.
- 'Belief in victory' -
He also said a US-led coalition air strike that killed at least 62 Syrian soldiers on September 17 was intentional "and not an error, even if the United States claims otherwise".
Rebel-held eastern districts came under intense air and artillery fire for a fifth night on Friday ahead of an anticipated ground offensive by the army to recapture the whole of the divided city.
Muallem told the UN: "Our belief in victory is even greater now that the Syrian Arab Army is making great strides in its war against terrorism, with the support of the true friends of the Syrian people," singling out Russia, Iran and Lebanon's Shiite militant group Hezbollah.
Saturday's death toll of 45 in Aleppo city was expected to rise because people remained trapped, said the Syrian Observatory for Human Rights, a Britain-based monitoring group.
It said another seven people were killed elsewhere in Aleppo province on Saturday.
"We were home when a missile crashed into our road," said one resident of the Bab al-Nayrab district who gave his name as Nizar.
Signup to our newsletter and follow us on Facebook and Twitter!
"Half of the building just caved in and our baby was hit on the head. He died on the spot," Nizar said, the body of his son on the ground wrapped in a blanket.
Seven people were killed in a strike as they queued to buy yoghurt at a market in the Bustan al-Qasr district on the front line dividing the government-held west from the rebel-held east of the city.
The attack left a pool of blood and body parts strewn across the site, said an AFP correspondent on the scene.
Medics said they were carrying out many amputations to try to save the wounded, while supplies of blood and IV drips were running out.
On Friday, at least 47 people were killed in heavy bombing, among them seven children, the Observatory said.
- Massive destruction -
There was massive destruction in several neighbourhoods, including Al-Kalasseh and Bustan al-Qasr, where some streets were almost erased by the bombardment.
Residents and activists said one type of bomb had produced earthquake-like tremors upon impact, razing buildings right down to their basements where many residents desperately seek safety during attacks.
The civil defence organisation known as the White Helmets was overwhelmed by the scale of the destruction, particularly after several of its bases were damaged by bombing on Friday.
With no electricity or fuel for generators, the streets of Aleppo are pitch black and difficult to navigate at night, and the fuel shortage has also made it tough to fill up vehicles.
The UN children's agency UNICEF said the loss of mains water posed serious health risks in rebel-held areas as the only alternative source of drinking water was from highly contaminated wells.
"It is critical for children's survival that all parties to the conflict stop attacks on water infrastructure," it said.
Further south in the central city of Homs, a convoy of 36 aid trucks reached the rebel-held district of Waer, the International Committee of the Red Cross said.
The denial of access to food, water and medicines has been used repeatedly as a weapon by all sides in the five-year war, which has cost more than 300,000 lives and displaced over half the population.
The approximately 250,000 people in east Aleppo have been under near-continuous siege since government troops encircled the area in mid-July.
A truce deal negotiated between Moscow and Washington brought a few days of respite in Aleppo earlier this month, but no humanitarian aid before its total collapse this week.