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 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 close to collapse.
Damascus's bid to recapture all of the divided northern city prompted the UN to warn of "a humanitarian catastrophe".
UN chief Ban Ki-moon announced he is setting up an internal board of inquiry to investigate the September 19 bombing of an aid convoy in Syria that killed 18 people.
The UN panel will report to Ban, who will "decide what further steps to take", a UN statement said.
Just over a week after Syria's army announced an operation to recapture all Aleppo, it was advancing both in northern and central Aleppo Friday, 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.
The Observatory said at least 15 people, including two children, were killed in strikes on Heluk and other eastern districts Friday.
- Humanitarian catastrophe -
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.
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.
Since the army operation began, Damascus and Moscow have pounded east Aleppo with air strikes, barrel bomb attacks and artillery fire, killing at least 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 besieged for most of the past two months.
It has been some of the worst violence since the March 2011 beginning of Syria's 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, a key ally of President Bashar al-Assad, began a military campaign to bolster his forces in September 2015 that has so far killed more than 9,300 people, the Britain-based Observatory says.
- 'Giant kill box' -
That figure includes 3,804 civilians and more than 5,500 jihadists and rebels, it says, adding that at least 20,000 civilians have been wounded.
The Observatory says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.
"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.
Kerry's Russian counterpart Sergei Lavrov on Friday accused Washington of protecting a jihadist group in its effort to overthrow Assad's regime.
Lavrov told the BBC that Washington had vowed, under a failed truce deal, to "take as a priority an obligation to separate the opposition" from the former Al-Qaeda affiliate Fateh al-Sham Front, once known as Al-Nusra Front, but that it had not done so.
"We have more and more reasons to believe that from the very beginning the plan was to spare Nusra and to keep it just in case for Plan B or stage two when it would be time to change the regime," Lavrov said.
Moscow said Thursday it would continue its campaign, 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.
