Sayyid Ali Khamenei is the current ruler of Iran, and is considered the Supreme Leader by the Shia. There is no person on the earth who is equal in rank to him, according to the Shia. Recently, this Supreme Leader of Iran launched his official website (www.leader.ir), wherein he answers questions and gives Fatwas.
In response to a question about Mutah, Grand Ayatollah Khamenei responded and declared that Mutah (temporary marriage) is not only permissible but rather it is Mustahabb (highly recommended). Ayatollah Khameini said:
“Although mut‘ah marriage is permissible, or rather mustahabb [highly recommended] in our view, it is not obligatory in shar‘[iah].”
(Source: https://www.leader.ir/langs/EN/tree/39/view.php?parent=n6986&catid=39)