Iran's Supreme Leader Ayatollah Ali Khamenei says he does not believe that groups protesting the presidential election results had foreign backing.

Iranian authorities have repeatedly alleged that defeated presidential candidate Mir Hossein Mousavi and other candidates were encouraged to cause political turmoil by nations plotting to destabilize Iran.

Wednesday evening, state television quoted Ayatollah Khamenei as saying he did not believe outside powers supported the protests. However, he said he thought the protests had been planned in advance of the election. 
Iran has been holding political trials for protest organizers, in which they publicly confess committing crimes against the state.

In Washington, the U.S. State Department called on Iran to release the only American citizen among the defendants - an Iranian-American academic.

A State Department spokesman said Kian Tajbakhsh, a social scientist and urban planner, still does not have a lawyer and poses no threat to the Iranian government. 

Earlier Wednesday, former President Mohammad Khatami said the public confessions of protest leaders are invalid because they are lies.

During Tuesday's trial, a key member of Iran's pro-democracy movement apologized for making what he called "major mistakes" during the election.

The defendant, Saeed Hajjarian, is one of several reformists being tried on charges of masterminding unrest following the highly contested re-election of President Mahmoud Ahmadinejad in June.

At the trial, Iran's prosecution asked the judge to ban two reform parties, the Islamic Iran Participation Front and the Mujahedin of the Islamic Revolution Organization.

Also Tuesday, a parliamentary committee said it would investigate reports that people killed in the post-election violence were secretly buried in a mass grave in Tehran.

Iranian lawmakers have said at least 30 people were killed in the deadly crackdown on election protests.

Thousands of people were arrested. Many have been released, but rights groups says the trials of the remaining detainees are a sham.

Some information for this report was provided by AFP and Reuters.