In a challenge to Iran's supreme leader Ayatollah Ali Khamenei, reformist Web sites on Monday reported that former president Mohammad Khatami has called for a national referendum to end the post-election crisis. Khamenei has declared the results of the elections valid, but supporters of Iranian opposition leader Mir Hossein Mousavi claim President Mahmoud Ahmadinejad won the election through mass fraud. Khatami said Iranians have lost their faith in the ruling political system following the June 12 election, and that a referendum would restore the government's legitimacy. It is too early to say whether Khatami's call for a referendum would be adopted by authorities, but it constitutes the latest challenge to Ayatollah Ali Khamenei, Iran's supreme leader who has the last word on state matters. Khamenei has declared the results of the elections valid.