ALEPPO, Syria (AFP) - The United States threatened on Wednesday (Sept 28) to suspend its engagement with Russia over the conflict in Syria following escalating attacks on rebel-held parts of Aleppo city, including strikes on two hospitals.
UN chief Ban Ki-moon denounced the attacks - which saw the two largest hospitals in Aleppo's opposition-controlled east hit with air strikes and artillery fire - as "war crimes".
President Bashar al-Assad's forces and his ally Moscow have carried out a barrage of air strikes on eastern Aleppo since Syria's regime announced a bid last week to retake all of the divided city.
Dozens of civilians have been killed, residential buildings have been reduced to rubble and residents of eastern districts - already suffering under a government siege - are facing severe shortages of food and medical supplies.
The latest bombardment has been some of the worst in Syria's five-year civil war, and comes after the failure of a short-lived ceasefire brokered by Russia and the United States earlier this month.
Moscow and Washington have traded blame over the truce's collapse, with stinging US criticism of Russia's participation in the Aleppo offensive.
On Wednesday, US Secretary of State John Kerry warned Russian counterpart Sergei Lavrov that Washington will end talks on the Syrian conflict unless Moscow halts the assault on Aleppo.
Kerry said the burden was on Russia to stop the assault and ensure humanitarian aid access, his spokesman John Kirby said.
"The United States is making preparations to suspend US-Russia bilateral engagement on Syria... unless Russia takes immediate steps to end the assault on Aleppo and restore the cessation of hostilities," Kirby said.
Wednesday's attack saw the M10 and M2 hospitals hit before dawn, forcing both to shut temporarily, said Adham Sahloul of the Syrian American Medical Society (SAMS), which supports both hospitals.
It was unclear who had carried out the bombings, which UN chief Ban denounced before the Security Council.
"Those using ever more destructive weapons know exactly what they are doing. They know they are committing war crimes," he said.
"Imagine the destruction. People with limbs blown off. Children in terrible pain with no relief," he said. "Imagine a slaughterhouse. This is worse."
Inside one of the hospitals, patients and medical staff cowered in fear.
"I am in the M2 hospital now. I was inside when the entrance to the emergency room was hit. Three of my colleagues were hurt," Aref al-Aref, a medical assistant, told AFP.
"Everyone is terrified and scared today. We are afraid that we will be today's victims."
Sahloul warned the attacks could have devastating consequences.
"With these two hospitals gone, if today there is another offensive like Saturday or Sunday, this is signing the death warrant for hundreds of people," he told AFP.
The World Health Organisation on Tuesday warned that medical facilities in the city's east were on the verge of "complete destruction" and urged humanitarian evacuation routes.
More than 170 people have been killed in east Aleppo since Syria's army announced its operation to retake the city, according to the Syrian Observatory for Human Rights, a monitoring group.
On Wednesday, at least six civilians died in artillery fire near a bakery in the opposition-controlled Maadi district, the Observatory said.
A hospital in the government-held west reported two people had been killed and 10 injured in rebel fire on the Aziziyeh district.
Clashes also continued inside Aleppo's Old City for a second day, the Observatory said, after pro-government troops seized control of the Farafira district north-west of Aleppo's historic citadel on Tuesday.
Once Syria's commercial hub, Aleppo has been ravaged by fighting and divided since mid-2012.
An estimated 250,000 people still live in the east, which has been under devastating siege by government forces since early September.
Rights groups and the opposition accuse the Syrian government and its allies of using sieges and deliberately targeting civilian infrastructure to pressure civilians to flee.
"There is no objective to attacking these hospitals other than adding to the suffering of civilians, destroying infrastructure so that civilians are left with no hospitals and are then forced to leave," said Diana Semaan, Syria campaigner at Amnesty International.
Last week, Syria's army urged civilians to flee to government-held territory but residents of the east fear passing through regime-held districts.
The head of the White Helmets volunteer rescue force, which operates in opposition-held territory in northern Syria, told AFP that under current conditions civilian facilities in eastern Aleppo would no longer be able to function within a month.
"The civilians there would seize any opportunity to escape, to go wherever they could go," Raed Saleh said.
"But nothing is available to provide safety and protection for those civilians. We are worried that they are facing massacre or the kidnapping or the arrest of many of them."