ALEPPO -  Residents in Syria’s battleground city of Aleppo cowered indoors Saturday as fierce airstrikes toppled buildings and killed at least 45 civilians, after diplomatic efforts to revive a ceasefire failed.

Nearly two million civilians were 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.

Rebel-held districts in east Aleppo came under intense air and artillery fire for a fifth night as the army prepared a ground offensive to recapture the whole of the divided city.

Saturday’s death toll of 45 was expected to rise because people remained trapped under rubble, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

“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. “Half of the building just caved in and our baby was hit in the head. He died on the spot,” Nizar said, as the body of his son lay 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 neighbourhood, which sits along 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 at the site, an AFP correspondent reported. Medics said they were carrying out many amputations to try to save the wounded and 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.

There was massive destruction in several neighbourhoods, including Al-Kalasseh and Bustan al-Qasr, where some streets were almost erased by the bombardment. Unexploded rockets were still buried in the roads in some areas, and elsewhere enormous craters were left by the bombing.

Residents and activists described the use of a missile that produced earthquake-like tremors upon impact and razed buildings right down to basement level where many residents desperately seek protection 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.

On Saturday morning, the streets were nearly empty, with just a few residents out looking for bread.

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 trucks carrying food and medicine reached the rebel-held district of Waer on Saturday, 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.

Meanwhile, Syria’s Foreign Minister Walid Muallem told the United Nations on Saturday that a US-led coalition airstrike on Syrian soldiers a week ago was intentional, rejecting US claims that it was a mistake. “The Syrian government holds the United States fully responsible for this aggression, because facts show that it was an intentional attack, and not an error, even if the United States claims otherwise,” Muallem told the General Assembly.

Dozens of Syrian soldiers were killed in the bombing on September 17 of the Syrian air base near the eastern city of Deir Ezzor, which is controlled by Islamic State (IS) militants.

The United States has expressed regret for the loss of lives, saying the coalition believed it was hitting an IS target and has promised to investigate the incident.

Muallem said the “cowardly aggression clearly proves that the United States and its allies are complicit with ISIL and other terrorist armed organizations.”

The coalition strike which involved US, British and Australian warplanes prompted the Syrian army to end a week-long truce that had raised hopes that diplomatic efforts to end the five-year war were bearing fruit.

More than 300,000 people have died in the conflict in Syria and millions have been driven from their homes.

Muallem hit out at Qatar and Saudi Arabia, accusing them of “sending into Syria thousands of mercenaries, equipped with the most sophisticated weapons” to fight President Bashar al-Assad’s government.

He said Turkey was allowing “tens of thousands of terrorists from all around the world” to cross its border into Syria, providing them with logistical support and training camps “under the supervision of Turkish and western intelligence.”