Al Jazeera said seven people died after inhaling a gas sprayed by government forces in a part of Homs held by the rebel Free Syrian Army. “We don’t know what this gas is but medics are saying it’s something similar to sarin,” rebel Raji Rahmet Rabbou told the Qatar-based news organization.

The “poisonous material” was deployed by government warplanes, Haaretz reported, citing a rebel statement.

Al Jazeera posted two videos it said were obtained from “a field clinic in the city.” The graphic videos indeed appear to depict victims of sarin or some other nerve agent — though again the origins and contents of these videos have yet to be verified by other sources.

Sarin can cause paralysis, choking and even death.