The Russian military informed the United States that rebels in the Syrian city of Aleppo launched an attack using toxic substances at 19:05 on Aug. 2, Interfax news agency reported on Wednesday, citing a Russian general.
As a result of the attack, seven people died and more than 20 people were sent to hospital, Interfax reported.
The fighting in Aleppo between government and rebel forces saw the largest rebel assault so far, according to monitoring group the Syrian Observatory for Human Rights, followed by suspected chemical attacks on Tuesday the BBC reported.
On July 30 and 31, the rebels blew up a tunnel under regime forces stationed in the Ramousah district of the city. The Syrian army, however, has fought back, aided by Russian air strikes. The Syrian Observatory said that it has managed to retake five of the eight positions the rebels had captured.
The insurgents are trying to break a government siege of their territory, which is home to around 250,000 civilians.