Fatameh Karoubi claimed her son Ali was savagely attacked inside a mosque by hard-line militiamen amid a massive security crackdown during events Thursday marking the 31st anniversary of the Revolution.

“They beat him up and insulted him along with other people arrested…,” she wrote in an open letter to Supreme Leader Ayatollah Ali Khamenei appearing on prominent pro-reform websites Rahesabz and Sahamnews.

The websites also posted photos purportedly showing bruises across Ali Karoubi's back.

She said the country's rulers have resorted to “violence and cruelty” in attempts to wipe out dissent.

The letter reflects the anger and dismay of many opposition groups after authorities unleashed a massive security crackdown to prevent disruptions of state-backed celebrations of the 1979 revolution. There are now questions whether the opposition can rebound with more large-scale street demonstrations.

Ali Karoubi was hauled away during an attack on the motorcade of his father Mehdi Karoubi, who ran against President Mahmoud Ahmadinejad in last June's disputed elections. The elder Karoubi was not injured, but he abandoned plans to attend an opposition gathering that same day.

Ali's mother said her son was taken from the mosque to a security base, where he was beaten further before he was released. She wrote that one agent told Ali “his family would receive his corpse” if he was allowed to continue the punishment for another day.

She begged Khamenei to reverse the country's direction “before more people die.” Khamenei, however, has strongly backed Ahmadinejad and the nation's powerful Revolutionary Guard, which has led the assault on the opposition.

“Unfortunately these days we don't have a proper justice system or a Parliament who can truly defend people and their rights,” she wrote. “So I'm asking you to help the people.” Iranian authorities have confirmed at least 30 people have died in unrest since the disputed election in June, while the opposition and international human rights groups say the toll is at least 80.