‘People collapsed': mystery chemicals lobbed at Iran protestors - eyewitnesses

They described symptoms that they said went beyond those caused by conventional tear gas, including severe breathing difficulties, sudden weakness and loss of movement.

“What was fired was not tear gas,” one protester said.

Iranian authorities crushed unrest earlier this month in the deadliest crackdown on protestors in the Islamic Republic's nearly 50-year history.

According to accounts, the gases caused intense burning of the eyes, skin and lungs, along with acute respiratory distress, repeated coughing, dizziness, loss of balance and, in some cases, vomiting or coughing up blood.

Witnesses said the severity and persistence of the symptoms differed from their past experiences with tear gas, although they said they could not identify the substances used.

Gas fired into crowds and escape routes

Witnesses said gas canisters were fired into crowds and along escape routes, including narrow streets and alleys.

According to the accounts, in some cases gunfire began at the same time, or immediately after, protesters lost the ability to walk or run and fell to the ground.

Several witnesses said that moments of immobilization became points at which shooting intensified, particularly when protesters collapsed in alleys or while trying to flee.

Reports came from multiple cities, including Tehran, Isfahan and Sabzevar.

Videos received from Sabzevar, a city in Razavi Khorasan province in northeastern Iran, and reviewed by Iran International showed security personnel wearing special protective clothing and masks designed for hazardous chemical materials, positioned on military-style vehicles in city streets.