DAMASCUS — Syria’s army took control of a rebel-held district in central Aleppo on Tuesday, after days of heavy air strikes that have killed dozens and sparked allegations of war crimes.

In the first advance since announcing plans last week to retake all of the divided city, pro-government troops seized the Farafira district northwest of Aleppo’s historic citadel, a military source said.

"After neutralising many terrorists... units are now demining the area," the source said.

The push follows several days of Syrian and Russian air strikes on rebel-held Aleppo neighbourhoods - some of the fiercest bombardment of the five-year conflict so far - after a ceasefire deal brokered by Moscow and Washington collapsed last week.

The Aleppo maelstrom prompted Western powers to accuse Russia of committing possible war crimes, charges the Kremlin condemned as "unacceptable".

In the latest broadside, NATO Secretary General Jens Stoltenberg also condemned the air campaign.

"The appalling attacks on Aleppo have shaken all of us, and the violence and the attacks we have seen... is morally totally unacceptable and is a blatant violation of international law," Stoltenberg told a news conference in Bratislava.

On the ground in eastern Aleppo, an AFP correspondent said air strikes struck several neighbourhoods simultaneously, including in Al-Shaar, where a five-storey building was levelled with a family stuck inside.

One young girl, her body encased in rubble, was among the dead. Her father, in shock as rescue workers picked up her lifeless body, collapsed beside her, saying: "She’s just sleeping. She’s just used to sleeping."

As well as the intensified violence, residents have been left reeling from food shortages and skyrocketing prices.

The World Health Organization warned that medical facilities in east Aleppo were on the verge of "complete destruction".

"Over the last weekend alone, more than 200 people were injured and taken to understaffed health facilities in east Aleppo," a spokeswoman said in Geneva.

The UN body called for "an immediate establishment of humanitarian routes to evacuate sick and wounded from the eastern part of the city."

The Syrian Observatory for Human Rights, a Britain-based monitor, said that there were "significantly fewer" strikes on Aleppo on Tuesday than in recent days, but confirmed the advance by pro-government forces into Farafira.

Aleppo has been roughly divided between government control in the west and rebel control in the east since mid-2012, and the frontline has remained largely static despite continuous violence.

Earlier this month, a ceasefire went into effect across Syria, brokered after exhaustive talks between US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov.

It was dubbed by Kerry as the "last chance" to end more than five years of devastating conflict.

But it fell apart within a week, with each side blaming the other for the latest failure in a war that has cost more than 300,000 lives since March 2011. — AFP