SAN FRANCISCO (Reuters) - Egyptians say the Twitter Web site is blocked on all Internet Service Providers in their country, a representative of Harvard University’s Herdict Web monitoring service told Reuters on Tuesday.

But Twitter users within Egypt are currently sending Tweets, short 140-character messages, via SMS text messages and through third-party applications, the center said as thousands of Egyptians took to the streets to protest President Hosni Mubarak’s 30-year rule.

Jillian York, a project coordinator at Harvard’s Berkman Center for Internet & Society, which runs the Herdict Web accessibility monitoring service, said in an email that she had “confirmed with users in Egypt that Twitter.com is in fact blocked on all ISPs.”