 Justifying the attack on Iran, Saddam Hussein accused Iranians of "murdering the second (Umar), third (Uthman), and fourth (Ali) Caliphs of Islam".In March 1988, Saddam Hussein killed about 20,000 Iranian soldiers immediately using nerve-gas agents.According to Iraqi documents, assistance in developing chemical weapons was obtained from firms in many countries, including the United States, West Germany, the United Kingdom, France and China.