The Russian military says Syrian militants have used a toxic agent against civilians in Aleppo, killing seven and sickening another 23 people.

The head of Russian military's Reconciliation Center at the Hemeimeem air base in Syria, Lt. Gen. Sergei Chvarkov, said Wednesday that the rebels struck a residential area in eastern Aleppo with a toxic agent. Chvarkov didn't identify the substance used in Tuesday's attack, but said the victims suffocated or suffered lung burns.

Chvarkov said the attack was launched by Nour el-Deine Zengi, a militant group he said has been considered by the U.S. as part of moderate opposition. He said the Russian military had informed the U.S. about the incident.

Nour el-Deine Zengi didn't immediately issue a response to the allegations.