DAMASCUS, Syria — At least 50 civilians were being treated Saturday following a suspected poison gas attack by Syrian rebel groups on the government-held city of Aleppo in the country’s north, according to reports in Syrian state media.

Most of those admitted to hospitals had breathing problems and blurred vision, doctors told state TV. One doctor said two were in critical condition, including a child.

Rebel commanders and opposition figures discredited the government reports, denying they lobbed gas into Aleppo and accusing Damascus of seeking to undermine an existing cease-fire and efforts to kickstart political talks. Earlier Saturday, government shelling of a rebel-held area in neighboring Idlib province killed at least seven civilians.

In Aleppo, local governor Hussein Diab visited the injured at a hospital. He told state TV that 41 people had been admitted and accused rebels of using poisonous gas in the missiles they lobbed at the Aleppo neighborhood. Health official Haj Taha later said the number of injured was up to 50, adding that symptoms suggest the gas used was chlorine. Further tests are needed, he said.

State TV said government troops retaliated, hitting the source of the attack. It didn’t elaborate.

A cease-fire in Aleppo and Idlib has been fraying in recent days. Aleppo has come under rebel attack in recent weeks, with missiles falling inside the city. The government has responded with counter attacks on rebel-held areas in the Aleppo countryside.

The opposition fighters don’t have chemical weapons or the means to create them, rebel commander Abdel-Salam Abdel-Razek said. On Twitter, he accused the government of staging the attack to frame the rebels.

In the absence of independent monitors, it is difficult to corroborate gas attacks. But both sides of the conflict have accused each other throughout the war of using poison gas.

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 the nerve agent sarin in an attack in April 2017 in the town of Khan Sheikhoun that killed about 100 people. The U.S. launched a series of strikes on Syrian government sites in retaliation for the attack in Khan Sheikhoun.

Albert Aji is an Associated Press writer.