Iranian authorities electronically jammed Yahoo! Messenger, the BBC World News and Persian TV, as the Guard continued to blackout communications following the controversial election, according to the UK's Guardian newspaper.
The Guardian reports bloggers and other media have been forced to remove any materials that "create tension" from their web sites, including profiles on Facebook and Twitter.
At least 20 sites aligned with Mousavi have been blocked, while some Iranian social networking users are reportedly able to update and access accounts via proxy servers.
Yahoo! Messenger played an important role since the election as Iranian officials began blocking the country's media and mobile phone infrastructure, said the Guardian's Leigh Holmwood and Saeed Kamali Dehghan in Tehran.
"Yahoo Messenger was one of the most important means that Iranians could still distribute information after the government filtered Facebook and Twitter," an Iranian graduate told the paper.
Clashing demonstrators have stirred rioting, which has left seven people dead and many more wounded, according to state-run media.
Journalists, human rights activists and dignitaries across the U.S. and other countries have questioned the legitimacy of Ahmadinejad's re-election based on alleged irregularities during the vote.
The Guardian's web site has reported the main electoral authority has offered to conduct a limited recount based on areas where such irregularities were reported; the challenger, Mousavi, responded by calling the election an "astonishing charade."
