The Central Intelligence Agency (CIA) worked in Iran to create 1953 riots which led to the removal of Prime Minister Mosaddegh. The United States and Great Britain then made the Shah Mohammad Reza Pahlavi the most powerful person in Iran, again. The Shah left Iran in 1979 in the face of a revolt. The Iranian government was changed to an Islamic Republic by Islamic Revolution. Soon afterwards, the Iranian Students Movement (Tahkim Vahdat), with the backing of the new government, took over the U.S. Embassy in Tehran. They held most of the diplomats hostage for 444 days.