Mojtaba Khamenei is a surprise appointment, but his accession is above all a statement of defiance, says Sina Toossi of the Center for International Policy

Many expect the 56-year-old, who has largely kept a low profile, to continue his father's hardline policies.

Iran appoints Mojtaba Khamenei as new supreme leader, succeeding his father amid tensions with the U.S. and Israel.