Security forces clashed with opposition protesters gathered Wednesday for a memorial for Iran's most senior dissident cleric, beating men and women and firing tear gas, reformist Web sites reported.

The gathering at the main mosque in the central city of Isfahan, 200 miles southeast of Tehran, was meant to honor Grand Ayatollah Hossein Ali Montazeri, the spiritual leader of the Iranian reformist movement who died Sunday.

His death set off large memorial ceremonies that turned into pro-opposition protests in defiance of a monthslong government crackdown on protesters rallying against the disputed June presidential elections. Iran has been in turmoil since the vote, which the opposition alleges Mahmoud Ahmadinejad won by fraud.

More than 50 people were arrested Wednesday in Isfahan, including pro-opposition cleric Masoud Adib, who was expected to address the gathering at the mosque, the Salaamnews and Parlemannews Web sites said.

Mourners poured out in thousands into the streets leading to the mosque, although anti-riot police and plainclothes pro-government Basij militiamen had blocked the neighborhood, the Web sites said.

Parlemannews reported that Basij beat people, including women, and used tear gas and pepper spray to disperse the crowds. It said troops also surrounded the home of Ayatollah Ayatollah Jalaleddin Taheri, a senior reformist cleric who organized the memorial.

Farid Salavati, an Isfahan resident who tried to attend the memorial, said anti-riot police and militiamen surrounded the Seyed Mosque since early morning.

"They didn't allow anybody to enter the mosque," Salavati told The Associated Press. "Tens of thousands gathered outside for the memorial but were savagely attacked by security forces and the Basijis."

Salavati said baton-wielding riot police clubbed people on the head and shoulders, and kicked men and women alike, injuring dozens. He said sporadic clashes were still going on by mid-day Wednesday. The memorial did not take place, he said.

"I saw at least two people with blood pouring down their face after being beaten by the Basijis," Salavati added.

The reports could not be independently confirmed. The authorities have banned foreign media from covering gatherings in any way connected to the opposition movement.

Taheri, the cleric who organized the service, was quoted by the Web sites as saying that "treating people this way at a memorial service is deplorable."

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.

The ceremonies in Montazeri's honor have became a show of defiance against the country's rulers. Tens of thousands of demonstrators had filled the main boulevards in Qom, the hub of Islamic scholarship and study in mostly Shiite Iran, for his funeral procession Monday.

Montazeri's death came as Iran marks one of the most important periods on the Shiite religious calendar, Ashoura. It culminates on Sunday, the same day mourners will gather for the traditional seven-day memorial for Montazeri, raising concerns of more violence.

Opposition leaders have used holidays and other symbolic days in recent months for anti-government rallies. Montazeri, who died of apparent natural causes on Sunday at age 87, had stunned even hard-core protesters with his scathing denunciations of the ruling clerics and their efforts to crush dissent after the June election.

His open assault on the highest reaches of the Islamic system helped galvanize the opposition and shatter taboos about criticizing the pinnacle of power, Iran's Supreme Leader Ayatollah Ali Khamenei.

Iran's opposition leader Mir Hossein Mousavi, who was defeated in the presidential election, also attended Montazeri's funeral.

On Tuesday, Iranian state television Web site said Ahmadinejad had appointed a new chief of Iran's prestigious Art Academy, removing opposition Mousavi from the post.