Iranian President Mahmoud Ahmadinejad began his second term in office Wednesday, as hundreds of opposition supporters took to the streets to demonstrate against his re-election.

Mr. Ahmadinejad was sworn in Wednesday in Tehran at an inauguration ceremony with members of Iran's parliament attending.

There were notable absences, including former president Akbar Hashemi Rafsanjani and defeated reformist candidate Mir Hossein Mousavi.

Mr. Ahmadinejad heralded his re-election as an "unprecedented epic" victory for the Iranian people and the Islamic establishment.

Iranian state-run media report thousands of security forces were deployed near Parliament to stop demonstrators from gathering.  Witnesses said police detained several protesters in the capital and used tear gas to break up demonstrations that coincided with the inauguration. 

Iranian media also report authorities have arrested one of Mr. Mousavi's aides.  Mir Hamid Hassanzadeh, who ran Mr. Mousavi's official Web site during the election campaign, was detained late Tuesday. 

Iranian opposition groups say the June 12 election was fraudulent, while the government says the election was fair. 

On Tuesday, Iranian reformist and former presidential candidate Mehdi Karroubi vowed that protests against the re-election of Mr. Ahmadinejad will continue. 

The United States, Britain, France, Germany and Italy have snubbed Mr. Ahmadinejad's re-election by declining to send congratulatory messages.  In Tehran Wednesday, the president addressed those countries' leaders indirectly, saying, "No one in Iran is waiting for your messages."

Britain defended its decision to have its envoy Simon Gass attend the inauguration, saying it is necessary to keep channels of communication open with Iran to address issues of concern.

In the United States, White House Spokesman Robert Gibbs distanced himself from a comment he made Tuesday in which he referred to Mr. Ahmadinejad as Iran's "elected leader." 

Gibbs told reporters Wednesday that it was not his place to pass judgment on the validity of the election.  He said it is up to the Iranian people to decide whether the election was fair.

A U.S. State Department spokesman said clearly the Iranian people still have "a lot of questions" about the election and Mr. Ahmadinejad's ability to lead.  But he said the United States will deal with an Iranian government that is willing to engage with the United States.

Iranian media report a mass trial is scheduled to resume Saturday for about 100 prominent reformist activists and political figures accused of trying to topple Iran's government.

Hundreds of activists who claim the presidential election was rigged were arrested after the vote in street protests that have been compared to the unrest that led to the 1979 Islamic Revolution.

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