Ayatollah Ali Khamenei has spent almost four decades as Shi'ite Iran's supreme leader building a regional power to rival the Sunni states across the Gulf and implacably hostile to the U.S. and Israel - while crushing repeated unrest at home.

President Donald Trump vetoed a plan presented to the U.S. in recent days to kill Iranian supreme leader Ayatollah Ali Khamenei, according to a U.S. official familiar with the matter.