He was stood up against the authority of regime. He believed that the repentance of Shah was as fake as Pharaoh's. No one had the firm purpose of overthrowing Pahlavi dynasty more than Imam Khomeini.
No one else believed it was possible. So they went to Imam many times to discourage him. He always told them not to fear from the United States.
(Robert Ernest Huyser Military Airlift Command from America)