Moscow: The Russian defence ministry on Wednesday said that seven people died in an attack by Syrian rebels in the battleground city of Aleppo using weapons loaded with a "poisonous agent".
Lieutenant-General Sergei Chvarkov was cited by Russia`s TASS news agency as saying that the Nureddin al-Zenki rebel group on Tuesday launched weapons packed with an unnamed "poisonous agent" from an opposition-held neighbourhood to a government-controlled area of Aleppo.
Chvarkov, the head of Russia`s reconciliation centre in Syria, said that "as a result of this terrorist attack, seven people died and 23 were evacuated to hospitals in Aleppo with breathing problems and airway burns."
He said the Russian authorities have informed the United States, which backs the rebels, of the attack.
Syrian state media said on Tuesday that five people were killed and that eight others suffered injuries induced by suffocation after rebels fired rockets containing poison gases.
The Syrian Observatory for Human Rights put the toll from the rocket attack at six dead, saying the casualties were in fact soldiers.
Speaking to AFP, Observatory director Rami Abdel Rahman could not confirm that any kind of gas had in fact been used.
The Russian claim came a day after the Observatory reported 24 people suffered breathing difficulties in rebel-held Saraqeb, a town 50 kilometres (30 miles) south of Aleppo, after a barrel bomb attack.
Residents said chlorine gas had been used in the attack, but the monitor could not confirm this.
The world`s chemical watchdog on Wednesday voiced concerns over reports of the use of chlorine gas in Saraqeb.
The incident in Saraqeb took place close to where Russia said on Monday one of its military helicopters was shot down, killing the five people on board.
Chvarkov said meanwhile that 372 Syrian civilians have used the "humanitarian corridors" set up by Russia to flee rebel-held areas of Aleppo to government-controlled turf.
He also accused rebels of trying to prevent people from leaving the areas of the city under their control.
In a statement on Tuesday, 35 NGOs called the humanitarian corridors initiative "deeply flawed".
The UN says 300,000 civilians still live in rebel-held parts of Aleppo city, despite four years of fighting and near-daily bombing.