Iran's supreme leader Ayatollah Ali Khamenei has ordered an investigation into claims of fraud in last week's presidential election.
The country's state television reported Ayatollah Ali Khamenei is ordering the powerful Guardian Council to examine the allegations by pro-reform candidate Mir Hossein Mousavi, who claims there was widespread vote rigging in Friday's election.
The Iranian government declared President Mahmoud Ahmadinejad the winner in a landslide victory.
It is a stunning turnaround for Iran's most powerful figure, who previously welcomed the results.
On Sunday, Mousavi wrote an appeal to the Guardian Council, a powerful 12-member body that is a pillar of Iran's theocracy. He also met with Khamenei.
Mousavi's backers have waged three days of street protests in Tehran.