Tens of thousands of democracy activists took to the streets of Tehran today chanting "death to the Dictator" and calling for an end to their Ayatollah-led "religious dictatorship." Their chants were met with the brutal violence of Basij militiamen and anti-riot police who used steel batons, fired bullets, and dropped tear gas on the crowd. "This was the most violent protest we've had by far, and people were also really angry and fearless," one witness in Tehran said.

According to the Telegraph, Tehran's city center is under lock-down.

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"Freedom is near, join us in the streets," a protester defiantly wrote on the Facebook page created for today's protests.

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The WSJ reports:

Witnesses said mobs of anti-riot police and plainclothes Basij militia lined the streets and on several occasions fired directly into the crowd and beat protesters with steel batons. In one neighborhood, the Basij took over a commercial building and dropped tear gas canisters from the roof onto the protesters, witnesses said.

Basij militia dressed in black shot and killed two young men in Tehran's Vanak and Vali Asr squares, according to witness accounts posted on opposition websites. The victims haven't been identified. Dozens have been injured and arrested, according to witnesses.

"This was the most violent protest we've had by far, and people were also really angry and fearless," said one witness from Tehran, adding that the public seemed resolved to stay on the street.

Opposition called for a mass demonstration on Sunday to commemorate the seventh day of mourning for two slain students, Sanah Jaleh, 26 years old, and Mohamad Mokhtari, 22, who were shot dead on Monday when security forces attacked a crowd.

The opposition movement is banking on momentum created by a wave of antigovernment uprisings across the Middle East, as well as public uproar at the killing of the two students and the government's attempt to exploit their deaths by claiming falsely they supported the regime.

"Freedom is near, join us in the streets," said one posting on the Facebook group created for Sunday's demonstrations.

"Step outside your door, every street is Freedom Square," said another.

In Tehran, protesters targeted government buildings such as the national broadcast company Seda va Sima—seen as a mouthpiece for the regime— chanting "God is great" and "Death to the dictator," witnesses reported on opposition websites.

Like the Libyan protesters, those in Iran gathered today to mourn two Iranian activists slain by government forces earlier this week.