Security forces and hard-line militiamen assaulted opposition protesters, beating men and women and firing tear gas, as thousands gathered in a central Iranian city for a memorial commemorating the country's most senior dissident cleric, who died this week.

The government's crackdown showed signs of moving for the first time against clerics who support the opposition: Basij militiamen surrounded the house and office of two prominent religious figures, shouting slogans and breaking windows, opposition Web sites reported.

The death on Sunday of the 87-year-old Grand Ayatollah Hossein Ali Montazeri, a sharp critic of Iran's leaders, gave a new push to opposition protests, which have endured despite a heavy security crackdown since disputed presidential elections in June.

His memorials have brought out not only the young, urban activists who filled the ranks of earlier protests, but also older, more religious Iranians who revered Montazeri on grounds of faith as much as politics. Tens of thousands marched in his funeral procession in the holy city of Qom on Monday, many chanting slogans against the government.

Wednesday's violence erupted when thousands tried to gather for a memorial to Montazeri at a mosque in the central city of Isfahan, 200 miles (325 kilometers) south of Tehran. They were met by a large force of riot police and Basijis, which stormed the crowds to disperse them, according to a witness and opposition Web sites.

Farid Salavati, an Isfahan resident who tried to attend the memorial, said baton-wielding riot police clubbed people on the head and shoulders, and kicked men and women alike, injuring dozens.

"They didn't allow anybody to enter the mosque," Salavati told The Associated Press. "I saw at least two people with blood pouring down their face after being beaten by the Basijis."

"Tens of thousands gathered outside for the memorial but were savagely attacked by security forces and the Basijis." He said sporadic clashes continued into the early afternoon, and the memorial at the Sayed Mosque was canceled.

More than 50 people were arrested in the Isfahan clashes, including pro-opposition cleric Masoud Adib, who was expected to address the gathering at the mosque, the Salaamnews and Parlemannews Web sites said. Parlemannews reported that Basijis beat people, including women, and used tear gas and pepper spray to disperse the crowds.

The reports could not be independently confirmed. Iranian authorities have banned foreign media from covering protests.