BEIRUT - Syrian regime forces advanced in the battleground city of Aleppo Friday, backed by a Russian air campaign that a monitor said has killed more than 3,800 civilians in the past year.
The UN has warned a humanitarian catastrophe is unfolding in Aleppo unlike any witnessed so far in Syria's brutal five-year war, which has claimed more than 300,000 lives
The Doctors Without Borders (MSF) charity accused Syria's government and its ally Moscow of provoking a "bloodbath" in the city, saying the eastern rebel-held portion had become "a giant kill box".
Syria's army was advancing on two Aleppo fronts, as talks between key players Washington and Moscow -- which back opposing sides in the war -- appeared on the verge of collapse.
Damascus's bid to recapture all of the divided northern city prompted the UN to warn of "a humanitarian catastrophe".
Just over a week after it announced an operation to recapture all of Aleppo, the army was advancing both in northern and central Aleppo, according to the Syrian Observatory for Human Rights monitor and state media.
In the north, it recaptured the Handarat former Palestinian refugee camp, as well as the old Kindi hospital, said Observatory director Rami Abdel Rahman.
Rebels had held the hospital since 2013, and capturing it allows government forces to threaten the opposition-held Heluk and Haydariyeh neighbourhoods in northeast Aleppo.
"The regime's strategy is to chip away until it reaches the heart of the rebel-held areas," Abdel Rahman said.
In central Aleppo, meanwhile, fierce clashes shook the Suleiman al-Halabi neighbourhood, which is divided by the frontline separating the rebel-held east and regime-held west.
- Humanitarian catastrophe -
The army is seeking to capture the opposition-held sector of the district and advance to the main water supply station for the government-controlled part of Aleppo which is in the neighbourhood.
State television said 15 civilians had been killed and 40 wounded by rocket fire into the government-held part of Suleiman al-Halabi and neighbouring Midan district.
The Observatory and an AFP correspondent on the ground said air strikes on Friday were focused on the battlefield, unlike in previous days which saw heavy bombardment of civilian areas.
Since the army operation began, Damascus and Moscow have pounded east Aleppo with air strikes, barrel bomb attacks and artillery fire, killing 216 people, including more than 40 children, according to the Observatory.
The assault has levelled apartment blocks and put hospitals out of service, creating a humanitarian catastrophe in opposition areas that have been under siege for most of the past two months.
It has been some of the worst violence since the March 2011 beginning of the conflict, which has killed more than 300,000 people and displaced over half the population.
Outside Damascus, meanwhile, air raids on several rebel-held towns in the Eastern Ghouta region killed at least 17 people including eight children, the Observatory said.
On Thursday, US Secretary of State John Kerry warned Washington was "on the verge" of suspending talks with Russia on Syria because of the Aleppo assault.
Moscow is a key ally of President Bashar al-Assad and began a military campaign to bolster his forces last September that has so far killed more than 9,300 people, the Observatory says.
That figure includes 3,804 civilians and more than 5,500 jihadist and rebels, according to the monitor.
At least 20,000 civilians have been wounded in the Russian raids, it said.
- 'A giant kill box' -
The Observatory -- which relies on a network of sources inside Syria for its information -- says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.
Moscow shrugged off the claims as non-credible.
"We do not consider as reliable the information... coming from this organisation, which is based in the United Kingdom," Kremlin spokesman Dmitry Peskov told reporters.
Moscow said Thursday it would continue its bombing campaign in Syria, despite Washington's threat and international concern about Aleppo.
"Bombs are raining from Syria-led coalition planes and the whole of east Aleppo has become a giant kill box," MSF director of operations Xisco Villalonga said in a statement on Friday.
"The Syrian government must stop the indiscriminate bombing, and Russia as an indispensable political and military ally of Syria has the responsibility to exert the pressure to stop this," he said.
UN aid chief Stephen O'Brien on Thursday told the Security Council that Aleppo was descending into the "merciless abyss of a humanitarian catastrophe unlike any we have witnessed so far in Syria".
Save the Children, meanwhile, said Friday that the use of bunker-busting bombs meant it would be too dangerous for children to return to school this weekend, even to underground classrooms.
The "ferocious assault" on Aleppo could deprive almost 100,000 school-age children of an education said the charity, which supports 13 schools in the city, eight of them underground.