Warsaw Pact use of chemical weapons.

[Trooper]

"In December (1996), when the first American units crossed the East German, the situation drastically changed. The United States and the Soviet Union were at war, and CENTCOM's deployment would be delayed until after the first of the year (all available transport was needed to support the war in Europe).

General Suryakin took advantage of the situation. The lead division of the 7th Guards Army advanced into nortwestern Iran, and encountered fanatical resistance from the Pasdaran militia. The Soviets countered this by using chemical weapons on a massive scale as they had in China."

RDF Sourcebook page 4.