The Latest on the Syrian conflict (all times local):

12:45 a.m.

Syrian rebels have dismissed government accusations they used poison gas to attack government-held Aleppo city.

Rebel commander Abdel-Salam Abdel-Razak says the opposition doesn't possess poisonous gases or the capabilities to lob them. Abdel-Razak served in Syria's chemical weapons program before defecting to join the opposition in the early years of the conflict, which began in 2011.

Abdel-Razak tweeted that "These are lies" soon after reports emerged of an attack in Aleppo that injured dozens of people.

Rebel spokesman Mustafa Sejari dismisses the poison-gas claims. He says they came after government shells landed in rebel-held areas, violating a Russian-backed cease-fire. He says the government is trying to undermine the cease-fire.

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12:25 a.m.

A Syrian official says that at least 50 civilians were being treated Saturday following a suspected poison gas attack by Syrian rebel groups on the government-held Aleppo city in the country's north.

Syrian state TV previously said that 21 people had been injured, but people continued to arrive at a hospital in Aleppo where state TV was airing live.

Health official Haj Taha says at least 50 civilians have been injured.

Head of Britain-based Syrian Observatory for Human Rights Rami Abdurrahman said there was a stench of gas in Aleppo city after projectiles were fired.

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10:30 p.m.

Syrian state media is reporting that 21 civilians have been treated for breathing problems following a rebel attack it said involved projectiles filled with poisonous gas on the government-held city of Aleppo.

Syrian state TV aired footage late Saturday of the injured lying in hospital beds as doctors administered oxygen and other treatments.

State news agency SANA quoted a police officer in Aleppo saying the attack hit al-Khalidiya neighborhood. Syrian state TV later said the attack has also hit two other areas in the city and said a total of 21 people had been injured. State TV interviewed doctors in a hospital who said most people were suffering from breathing problems and blurred vision.

In the past, rebels have accused the government of using chlorine gas to attack opposition-held areas.

A joint team from the United Nations and the Organization for the Prohibition of Chemical Weapons accused Syria's government of using chlorine gas in at least two attacks in 2014 and 2015, and using the nerve agent sarin in an attack in April 2017 in the town of Khan Sheikhoun that killed about 100 people.

The UN-OPCW team also accused the Islamic State extremist group of using mustard gas twice in 2015 and 2016.