Beirut: Russian or Syrian warplanes knocked a major Aleppo hospital out of service on Wednesday, hospital workers said, and ground forces intensified an assault on the city's besieged rebel sector, in a battle that has become a potentially decisive turning point in the civil war.
Shelling damaged at least another hospital and a bakery, killing six residents queuing up for bread under a siege that has trapped 250,000 people with food running out.
The World Health Organization said it had reports that both hospitals were now out of service.
The week-old assault has already killed hundreds of people, with bunker-busting bombs bringing down buildings on residents huddled inside. Only about 30 doctors are believed to be left inside the besieged zone, coping with hundreds of wounded a day.
"The warplane flew over us and directly started dropping its missiles... at around 4am," Mohammad Abu Rajab, a radiologist at the M10 hospital, the largest trauma hospital in the city's rebel-held sector, told Reuters.
"Rubble fell in on the patients in the intensive care unit."
M10 hospital workers said oxygen and power generators were destroyed and patients were transferred to another hospital. There were no initial reports of casualties in the hospital.
Photographs sent to Reuters by a hospital worker at the facility showed damaged storage tanks, a rubble strewn area, and the collapsed roof of what he said was a power facility.
The government of President Bashar Al Assad has launched a massive assault to crush the rebels' last major urban stronghold.
Syria's largest city before the war, Aleppo has been divided for years between government and rebel zones, and would be the biggest strategic prize of the war for Assad and his allies.
Taking full control of the city would restore near full government rule over the most important cities of western Syria, where nearly all of the population lived before the start of a conflict that has since made half of Syrians homeless, caused a refugee crisis and contributed to the rise of IS.
The offensive began with unprecedentedly fierce bombing last week, followed by a ground campaign this week, burying a ceasefire that had been the culmination of months of diplomacy between Washington and Moscow.
Washington says Moscow and Damascus are guilty of war crimes for targetting civilians, hospitals, rescue workers and aid deliveries, to break the will of residents and force them to surrender. Syria and Russia say they target only militants.
UN Secretary-General Ban Ki-moon also said those using "ever more destructive weapons" were committing war crimes and that the situation in Aleppo was worse than "a slaughterhouse".
The Syrian army said a Nusra Front position had been destroyed in Aleppo's old quarter, and other militant-held areas targeted in "concentrated air strikes" near the city.
France's Foreign Minister Jean-Marc Ayrault said he was working to put forward a United Nations Security Council resolution to impose a ceasefire in Aleppo, and that any country that opposed it would be deemed complicit in war crimes.
"This resolution will leave everyone facing their responsibilities: those who don't vote it, risk being held responsible for complicity in war crimes," he said.
Another hospital, M2, was damaged by bombardment in the Al Maadi district, where at least six people were killed while queuing for bread at a nearby bakery, according to the Syrian Observatory for Human Rights monitoring body and residents.
Food supplies are scarce in the besieged area, and those trapped inside often queue up before dawn for food.
The collapse of the peace process leaves US policy on Syria in tatters and is a personal blow to Secretary of State John Kerry, who led talks with Moscow despite scepticism from other top officials in President Barack Obama's administration.
Washington says the offensive shows Assad and Russian President Vladimir Putin have abandoned negotiations in order to seek battlefield victory, turning their backs on an earlier international consensus that no side could win by force.
Assad's allies have said in recent days the war will be won in combat.
But the rebels remain a potent military force even as they have lost control of urban areas. The collapse of peace efforts ends a proposed scheme to separate Western-backed fighters from hardened militants.
The rebels' main demand has long been for the provision of anti-aircraft missiles, but Washington has resisted this, fearing they could end up in the hands of militants.
Fierce fighting accompanied by air strikes was reported on Wednesday in northern Hama province between rebels, the Syrian government and allied forces. The Syrian army is trying to recapture territory lost this week to insurgents who launched a major offensive to push down towards government-controlled Hama city at the start of September.
A senior official in Aleppo-based rebel group said pro-government forces were mobilising in apparent preparation for more ground attacks in central areas of the city.
"There have been clashes in Al Suweiqa from 5am until now. The army advanced a little bit, and the guys are now repelling it," a fighter in the rebel Levant Front group said in a recording sent to Reuters, referring to an area in the city centre where there was also fighting on Tuesday.
Another rebel official said government forces were also attacking the insurgent-held Handarat refugee camp a few kilometres to the north of Aleppo.
"It doesn't seem that their operation in the old city is the primary operation, it seems like a diversionary one so that the regime consumes the people on that front and advances in the camp," the official, Zakaria Malahifij, head of the political office of the Fastaqim group, told Reuters from Turkey.