Heavy fighting broke out between Syrian government forces and rebels in Aleppo on late Saturday, 22 October, after a three-day ceasefire announced by the regime's ally Russia expired, a UK-based monitor has said.

The Syrian Observatory for Human Rights said fierce clashes erupted in many areas along the front line in southwest of the city. The air strikes hit the opposition-held district of Sheikh Saeed in the first attack since the truce ended.

According to Reuters, there have been night-time clashes since the ceasefire ended but the fighting on Saturday was more fierce.

Ismail al-Abdullah, a volunteer of the white Helmets Syrian civil defence group and a resident of Aleppo, told the BBC that he had witnessed bombings just hours after the ceasefire ended.

Residents and rebels refused to heed calls from Syrian and Russian forces to leave the city during the ceasefire. The humanitarian pause began on Thursday, following Russia's announcement to halt the bombing campaign to take control of the entire city of Aleppo.

The Syrian army reportedly opened eight corridors for residents and rebels to leave, but only one passage was used that too by a handful of people.

Rami Abdel Rahman, head of the Observatory, said: "Members of popular civil committees from regime districts entered the eastern neighbourhoods to try to evacuate the injured but failed."

A official with the rebel Fastaqim Union told Reuters: "Nobody has left through the corridors. The small number of people which who tried to leave were faced with shelling around the (corridor area) and could not leave."

Rebels also said that during the ceasefire there is no relief available to those who want to remain in rebel-held areas of eastern Aleppo. They believe that the regime wants to get rid of political opponents from the cities, hence it agreed to the ceasefire.

Aleppo, once Syria's largest city, is now divided between the government-held west and rebel-held east. Eastern Aleppo has not received any humanitarian aid since early July, reports said. The United Nations hoped that ceasefires would allow aid deliveries, but the lack of security had stopped aid workers from going to troubled areas.

Jens Laerke, UN humanitarian spokesperson, said: "The UN remains hopeful that parties will provide all necessary guarantees and is actively working to that end. The situation on the ground remains volatile as exchanges of fire and clashes continue. Just today bullets struck the hotel where the UN hub is based and critically injured one hotel staff."

On Friday, at an emergency meeting of the UN in Geneva, human rights chief Zeid Raad al-Hussein said, "crimes of historic proportions", were being committed in eastern Aleppo and other places in Syria.