Iraq responded with counteroffensive, launching an airborne assault and employing the use of poison gas for the first time in the entire war. The Iraqis hit Iranian troops on mountain tops near Haj Omran with mustard gas while their troops advanced in the slopes. The Iraqis were unfamiliar with the properties of poison gas and the agent descended back down to the exposed Iraqi troops. At the same time, the rugged terrain held up Iraqi tanks. The use of helicopter gunships was also hampered, since the Iranian and Kurdish fighters had better cover.