Heavy clashes erupted between regime and opposition forces in Syria's divided city of Aleppo after a unilateral ceasefire announced by Russia expired, according to the Syrian Observatory for Human Rights (SOHR).

The first Syrian or Russian air strikes on Aleppo, Syria's most populous city before the war, since Russia began the pause in hostilities on Thursday hit a key frontline in the city's southwest.

Ground clashes and shelling, which had continued throughout the day on frontlines, intensified.

The pause began on Thursday, and came after Russia announced a temporary halt to the Syrian regime army's campaign to recapture the divided city.

Moscow had extended the unilateral "humanitarian pause" into a third day until 1600 GMT Saturday, but announced no further renewal of the truce despite a UN request for longer to evacuate wounded civilians.

The SOHR reported fierce fighting in several areas of Aleppo, with three people wounded by shelling of the opposition-held Salaheddin and Al-Mashhad districts.

No civilians were evacuated during the truce, Ingy Sedky, spokeswoman for the International Committee of the Red Cross in Syria, said, adding that evacuations were impossible due to the poor security situation in the city.

More than 2,000 civilians have been wounded since the regime army launched its offensive to drive the opposition forces out of the eastern districts they have held since 2012. Nearly 500 people have been killed.

About 250,000 to 300,000 civilians are thought to be trapped in eastern Aleppo, with dwindling food supplies and extremely limited medical care in underground hospitals that have themselves been hit repeatedly by air strikes.

The UN had hoped to use the ceasefire to evacuate seriously wounded people, and possibly deliver aid. But a UN official said the requisite security guarantees had not been received.

"You have various parties to the conflict and those with influence. They all have to be on the same page on this and they are not," said David Swanson, a spokesman for the UN humanitarian office.

No aid has entered Aleppo since July 7 and food rations will run out by the end of the month, UN chief Ban Ki-moon warned on Thursday.

The UN had asked Russia to consider extending the pause until Monday evening, but there was no word of any extension as the 1600 GMT deadline passed.

Russia is a key ally of Syria's regime and began a military intervention in support of Bashar al-Assad last September.

On Friday, a UN human rights council resolution called for "a comprehensive, independent special inquiry into the events in Aleppo".

It also demanded that warring parties provide unrestricted humanitarian access to desperate civilians and "end immediately all bombardments and military flights over Aleppo city".

Also Friday, UN experts said the Syrian army was responsible for a March 2015 chemical weapons attack on the village of Qmenas.

PHOTO CAPTION

Children play with water from a burst water pipe at a site hit by an air strike in Aleppo's opposition-controlled al-Mashad neighborhood, Syria, September 30, 2016. REUTERS

Al-Jazeera