Given the widely-acknowledged role of social media in the run-up to the vote in Iran, it’s no surprise that Twitter is now a key tool of protestors.

Protestors in Iran on Monday used Twitter for battle cries and to spread word about clashes with police and “hard line supporters” of President Mahmoud Ahmadinejad.

Twitter messages, some with links to pictures, streamed from Iran despite reported efforts by authorities there to block news of protests over Ahmadinejad’s claim of having been fairly re-elected.

UPDATE:  Here’s a Times article on the impact of social networks in Iran.