Rescuers in Syria said Tuesday a helicopter dropped barrels filled with toxic gas, seriously injuring dozens of people, not far from where a Russian transport helicopter was shot down the day before, Reuters reported.

A spokesman for rebel fighters reportedly said 33 people, most of them women and children, were hurt. They believed chlorine gas was used, but could not confirm it.

A video posted to YouTube apparently showed several men struggling to breathe in the aftermath. Russia and Syria did not immediately comment.

The Syrian National Coalition issued a statement that read: “After shelling, besieging and killing civilians and perpetrating war crimes on them, the Assad regime has resorted once again, and in breach of UN resolutions 2118 and 2235, to using chemical substances and toxic gasses.”

The Russian transport helicopter was shot down in opposition rebel territory on Monday and all five crew and officers onboard were killed, the Kremlin said.

The Mi-8 helicopter was shot down in Idlib province, where Russian warplanes frequently targeted rebels. The Russian Defense Ministry said in a statement that the chopper was returning to the Russian air base on Syria’s coast after delivering humanitarian goods to the city of Aleppo. But video uploaded by opposition activists showed a rocket pod next to the wreckage.

Dmitry Peskov, spokesman for Russian President Vladimir Putin, said the Russians “died heroically because they tried to move the aircraft away so to minimize losses on the ground.”

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