Aleppo faces catastrophe

* Obama 'not optimistic' after Putin meet 

* UN warns time running out as fear for civilians grow

Syrian regime forces advanced quickly in rebel-held areas of Aleppo yesterday, pressing a new offensive in defiance of international concern over the fate of the city and its residents.

Both US President Barack Obama and the UN's Syria envoy expressed pessimism about the future of the city, where more than 250,000 people are besieged in the rebel-held east.

More than 100 civilians have been killed in the east since the regime's latest offensive began on Tuesday, according to the Syrian Observatory for Human Rights monitor. A CNN report puts the number much higher at 300 including rebels and governmrnt forces.

The group said government forces backed by Iranian and Russian troops and fighters from Lebanon's Hezbollah had captured the eastern part of the Masakan Hanano neighbourhood.

"It is the most important advance inside the eastern neighbourhoods that the regime has made so far," said Observatory director Rami Abdel Rahman.

In mid-July, the regime surrounded the east, subsequently announcing an operation to recapture it completely.

Despite international outrage, including over the bombing of hospitals and rescue worker facilities, there has been little sign that foreign powers or the UN can stop the fighting in Aleppo.

Obama said Sunday he was "not optimistic about the short-term prospects in Syria".

"Once Russia and Iran made a decision to back (Bashar al-) Assad in a brutal air campaign... it was very hard to see a way in which even a trained and committed moderate opposition could hold its ground for long periods of time," he added after he briefly met Russian President Vladimir Putin on the sideline of Apec summit.

On Sunday, Syria's Foreign Minister Walid Muallem rebuffed a proposal from UN envoy Staffan de Mistura to halt fighting in Aleppo and allow the opposition to administer the east of the city.

Under the proposal, jihadist forces would have left east Aleppo, and both sides would cease fire.

The top UN diplomat warned that time was "running out" for eastern Aleppo, adding that there was concern "instead of a humanitarian or a political initiative" there would be "an acceleration of military activities" in the city and elsewhere.

The UN Security Council is scheduled to meet later Monday in New York to discuss humanitarian efforts in Syria.