Security forces and hard-line militiamen assaulted opposition protesters, beating men and woman 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 Teheran. 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. Security forces also surrounded the home of Ayatollah Jalaleddin Taheri, a senior reformist cleric who organized the memorial, several Web sites reported. "Treating people this way at a memorial service is deplorable," Taheri said in a statement. Later in the evening, his supporters forced their way through the cordon, scuffling with security forces, who eventually relented and moved from the area, Web sites reported. Taheri was the chief Friday prayer leader in Isfahan until he resigned in 2002 in protest against the establishment, which he said was paralyzing the country in the name of religion to maintain its hold on power. Meanwhile, for the past two nights, plainclothes hard-liners, thought to be Basijis, surrounded the office in Qom of another prominent pro-reform cleric, Grand Ayatollah Youssef Saanei, shouting "insulting slogans," tearing up posters and breaking windows, Saanei's office said in a statement carried on opposition Web sites. In the postelection crisis, Saanei has emerged as one of the most prominent critics of Iran's clerical leadership among the country's grand ayatollahs, the highest rank in the Shiite religious hierarchy. He denounced the crackdown launched after the June election, which the opposition says Iranian President Mahmoud Ahmadinejad won by massive vote fraud. Saanei and other reform clerics have been criticized by hard-liners in past months, but rarely have they come under direct harassment or pressure. The leadership may be particularly nervous about the fallout from Montazeri's death because it came as Iran marks one of the most important periods on the Shi'ite religious calendar, the first 10 days of the Islamic month of Moharram, a time of mourning rituals for a revered Shi'ite saint. The period culminates on Sunday with Ashoura - a day that coincides with the seventh day after Montazeri's death, a traditional day of further commemorations. That could fuel greater protests. Iran's police chief, Gen. Ismail Ahmadi Moghaddam, on Wednesday threatened tougher action against protesters and issued a warning against those in the opposition who he said "made a show of supporting" the Islamic republic - an apparent reference to the many pro-reform political leaders and clerics who are veterans of the 1979 Islamic Revolution that brought clerics to power. "Today, it has been proven to the people that they are moving in violation of [the Islamic Republic] and the law," he said, according to the semi-official Mehr news agency. "The hypocritical nature of this movement has become clear." "We once again urge them to stop their actions, or else severe action will be taken against them under the law," he said. Meanwhile, Ahmadinejad removed opposition leader Mir Hossein Mousavi from his official post as head of the Art Academy. Mousavi, who the opposition says was the true winner of the election, is an architect who has long been prominent in the arts scene. Iranian state television announced Wednesday that Ahmadinejad appointed a new head. Salaamnews said Ahmadinejad broke off a tour of southern Iran Tuesday to attend the meeting that sacked Mousavi. There have been concerns Mousavi could be arrested and tried, along with hundreds of opposition supporters now on trial for taking part in the protests. Pro-reform lawmaker Darioush Ghanbari said it was a "politically motivated decision" by the government. "It shows they can't tolerate Mousavi even" as part of the academy.