Mourners attend the funeral ceremony of Iranian Grand Ayatollah Hossein Ali Montazeri, the spiritual father of Iran's reform movement, in Qom, a city 125 kilometres south of Tehran. (Associated Press)

Tens of thousands of Iranian mourners joined the funeral procession Monday for the country's most senior dissident cleric, who repeatedly described the government's crackdowns on protests as the work of power-hungry despots.

Grand Ayatollah Hossein Ali Montazeri, a staunch defender of the country's opposition movement, died Saturday night at age 87, and police were standing by in three Iranian cities to handle any unrest.

Foreign media have been barred from covering the procession in the holy city of Qom, but witnesses report many mourners shouted protest slogans aimed at the country's ruling establishment, including "Death to the dictator."

Iranian state television made only a passing reference to Monday's funeral. However, videos of the event popped up across the web, firsthand reports that showed the inability of Iran's authorities to fully control the internet.

Online footage showed men beating their chests and chanting, "Oppressed Montazeri, you are with God now." Women in black robes shouted, "Dictator, dictator, Montazeri is alive," and "Montazeri, you who spoke the truth! Your path will be followed."

Some climbed onto tree branches for a better view of the procession — which included mourners clutching portraits of Montazeri, holding up green banners, and sporting wrist bands in a powerful show of support for the green movement of opposition leader Mir Hossein Mousavi.

Montazeri's body was buried in a shrine alongside his son, who was killed in a bomb blast in the early days of the Islamic Revolution.

Mousavi was among those in attendance at Montazeri's funeral.

Some reformist websites reported that mourners attacked Mousavi's car as he left Qom and noted at least one member of his entourage was injured. The reports could not be independently confirmed.

There were no reports of serious clashes from the witnesses, who spoke on condition of anonymity because of fears of arrest. Opposition websites noted some scuffles and violence, but no reports could be confirmed.

The New York-based International Campaign for Human Rights said Ahmad Ghabel, a government critic and follower of Montazeri, was arrested with his family on his way to Qom.

Montazeri was an architect of Iran's 1979 Islamic revolution, but for years he has been critical of Iran's leaders, accusing them of imposing dictatorship in the name of Islam. He persisted with his criticism after June's disputed presidential election, which kept incumbent President Mahmoud Ahmadinejad in power amid widespread demonstrations. Reformists were also planning to gather in Tehran and Montazeri's hometown, Najafabad.

Authorities faced a difficult choice over whether to try to prevent an outpouring at the funeral that could escalate into another street protest by the government's opposition. A crackdown would risk serious backlash from an influential group of clerics based in Qom who are among the current leadership's critics.

With files from The Associated Press