UN chief Ban Ki-moon said Saturday he was "appalled by the chilling military escalation" in Syria's battleground city of Aleppo where residents cowered indoors as air strikes toppled buildings and killed at least 45 civilians.

The Security Council was set to meet Sunday to discuss the upsurge in violence since the Syrian army announced an offensive to retake the rebel-held east of the devastated city.

Nearly two million civilians were left without water in Aleppo after regime bombardment damaged a pumping station and rebels shut down another in retaliation, the UN said.

Ban warned the use of bunker buster bombs and other advanced munitions against civilians may amount to war crimes, after the army Thursday launched the offensive backed by Russian air raids that has cost around 100 lives.

Top EU officials said that the attacks on civilians amount to a "breach of international humanitarian law," and called for intensified peace efforts.

Washington and leading European powers said Saturday that "the burden is on Russia... to salvage diplomatic efforts to restore a cessation of hostilities."

A week-long ceasefire agreed between the United States and Russia ended on Monday and efforts to revive the truce failed.

That same day, an aid convoy was hit by an air strike that US officials have said was carried out by Russian planes, although Moscow has denied responsibility.

- 'Cease bombing women and children' -

US Secretary of State John Kerry, who failed in talks with Russian counterpart Sergei Lavrov to revive the ceasefire, earlier 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 regime said it was confident of victory, with Foreign Minister Walid Muallem telling the UN General Assembly that the army and its allies were making "great strides" in the conflict.

He 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 of Aleppo 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 in the rubble, 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.

"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.

- Massive destruction -

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.

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.

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.

Missiles batter Aleppo as Syria army readies ground assault
Aleppo, Syria (AFP) Sept 23, 2016 - Missiles rained down on rebel-held areas of Syria's Aleppo on Friday, causing widespread destruction that overwhelmed rescue teams, as the army prepared a ground offensive to retake the city.

Nearly 30 civilians including several children were killed and dozens wounded in the raids by Russian warplanes and regime aircraft, said the Syrian Observatory for Human Rights, a Britain-based monitoring group.

The intensity of the bombardment, which included artillery barrages and barrel bombings by helicopters, brought new misery to the estimated 250,000 civilians besieged by the army.

The escalation came after US Secretary of State John Kerry failed to reach an agreement with Russian counterpart Sergei Lavrov on Thursday on terms to salvage a failed ceasefire.

The two met again on Friday at the United Nations and made what Kerry said was "a little bit of progress" on resolving their differences on Syria.

"We're evaluating some mutual ideas in a constructive way, period," Kerry told reporters.

Asked at the UN earlier whether the truce could be reinstated, Lavrov simply said: "You should ask the Americans."

He later told the UN General Assembly that US-Russian agreements aimed at ending the Syria conflict must be salvaged, saying there was "no alternative" to the process.

"Now it is essential to prevent a disruption of these agreements," Lavrov said.

Thursday's Kerry-Lavrov talks in New York broke up after Russia refused US demands that it promise to immediately ground the Syrian regime's air force.

- Assad 'playing partition card' -

Also in New York, French Foreign Minister Jean-Marc Ayrault accused Syrian President Bashar al-Assad of "playing the card of a partition" of his country with the Aleppo offensive.

An AFP journalist in rebel-held east Aleppo reported relentless air raids and artillery fire overnight and Friday morning.

Entire apartment blocks were flattened, overwhelming rescue teams from the White Helmets civil defence organisation.

In the Al-Kalasseh district, three buildings were levelled by a single strike, and rescue workers tried frantically to reach survivors using a single bulldozer and their bare hands.

The White Helmets' headquarters in the Ansari district was badly damaged along with an ambulance and a fire engine. A second centre operated by the group was also hit.

Rescue workers told AFP their stock of diesel was down to 2,000 litres (530 gallons), forcing them to ration fuel and make choices on when to intervene.

Also in Aleppo province, the Observatory reported 15 deaths including 11 children in a Russian raid on the rebel-held town of Beshkatine and 11 killed in raids by unidentified aircraft on Islamic State group stronghold Al-Bal.

The bombardment came a day after the Syrian army announced an offensive to recapture east Aleppo, which has been held by the rebels since mid-2012 but has been surrounded by government forces since July.

The army urged civilians to distance themselves from "the positions of terrorist groups" and pledged that fleeing residents would not be detained.

A high-ranking military source confirmed that the bombardment was preparation for a ground assault.

"We have begun reconnaissance, aerial and artillery bombardment," he told AFP.

"This could go on for hours or days before the ground operation starts. The timing of the ground operation will depend on the results of the strikes and the situation on the ground."

- Preparing ground operation -

The conflict in Syria has cost more than 300,000 lives and displaced over half the country's population since it erupted in March 2011.

In a bid to relaunch peace talks, Kerry and Lavrov announced a ceasefire on September 9, with Moscow responsible for forcing government troops to stand down and allow in UN aid convoys.

Washington was supposed to pressure rebel forces to respect the truce and distance themselves from jihadists, but the ceasefire fell apart acrimoniously and the Syrian army declared it over on Monday.

UN peace envoy Staffan de Mistura said Thursday's failed talks were "long, painful and disappointing" and warned of escalating violence.

In Geneva, the UN said Friday it was considering a different route to send desperately needed aid to east Aleppo to circumvent the blocked main supply route.

In Damascus, an analyst close to the regime said it was no coincidence that the Aleppo assault began as the New York talks broke down.

"In Aleppo, negotiations are being conducted by fire," he said.

"The Americans must understand that so long as they don't implement their commitments, particularly for the rebels to distance themselves from... (jihadists), the Russians and the Syrian army will advance."

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