Supporters of reformist presidential candidate Mir Hossein Mousavi carry his poster, during a rally in Azadi street in Tehran, 15 June 2009

Iranian opposition activists are using the popular messaging service Twitter to spread updates on the post-election tension in the streets of Tehran.

While the Iranian government has cracked down on foreign media, activists are using the Web-based service to send links to videos, photos and accounts of violence.  Twitter can be accessed through mobile phones and through different sites on the Internet, so users can get around government efforts to block access.

The Twitter posts are intended to inform the international community as well as to communicate with other activists within the country.

The service has been used primarily by supporters of defeated presidential candidate Mir Hossein Mousavi.  Many people have tinted their account icons green to show support for Mr. Mousavi, whose campaign used the same color.

Biz Stone, a co-founder of Twitter, announced Monday that the company's network host decided to delay a service upgrade to avoid disrupting service in Iran.

Twitter messages, called "tweets," are limited to 140 characters.  Hundreds of tweets on Iran are pouring in every minute over the Web site.

Messages on the Iranian election can be found at Twitter.com, marked with the tag #IranElection.