Syrian rebels have opened a new front in Aleppo as fighting spread on the third day of a major insurgent counter-attack to break the government's siege of the opposition-held part of the city, and each side has accused the other using poison gas.
The rebels, including both Free Syrian Army factions and jihadists, are seeking to end the siege by seizing government-held areas of Aleppo, in an effort to link the city's rebel-held east with rebel-held rural areas to the west of the city.
Syrian state media said militants had fired shells containing chlorine gas at a residential area of the government-held western part of the city, al-Hamdaniya. Rebels denied that, and said government forces had fired poison gas on another frontline.
State media cited an Aleppo hospital director saying three dozen people - civilians and soldiers - had suffered suffocation in the alleged rebel gas attack, but did not report any deaths.
The Syrian Observatory for Human Rights, a UK-based organisation that reports on the war, said it had confirmed reports of suffocation among government fighters in two frontline areas shelled by rebels, but it did not know if chlorine gas was the cause.
The rebels said the army had shelled rebel-held Rashideen district with chlorine and shared videos purportedly showing victims with respiratory problems.
Aleppo, Syria's biggest pre-war city, has become the main stage of conflict between President Bashar al-Assad, backed by Iran, Russia and Shi'ite militias, and Sunni rebels including some supported by Turkey, Gulf monarchies and the United States.
The city has been divided for years between the government-held western sector and rebel-held east, which the army and its allies put under siege this summer and where they launched a new offensive in September that medics say has killed hundreds.
The Observatory said at least 38 people including 14 children had been killed in rebel shelling of government-held areas of Aleppo in the last 48 hours.
Jaish al Fateh, a rebel alliance including powerful Islamist and jihadist factions, said in a statement they were now moving into a second stage of the offensive after taking several areas with the goal of "ending the siege".
They called on residents of government-held areas in western Aleppo to stay at home or in underground shelters as they spread their offensive, saying they were coming to "liberate" their land. They urged the fighters not to harm anyone who did not carry arms.