Iranian opposition leaders are calling for a public day of mourning Monday for dissident cleric Grand Ayatollah Hossein Ali Montazeri.
The outspoken senior cleric was reported to have died at home of a heart attack before dawn on Sunday. He was 87.
Witnesses say thousands of people are traveling to Qom for a funeral, and some already have started gathering outside Ayatollah Montazeri's home.
Reformist Web sites are urging supporters to gather in Qom and in Tehran's public squares for a day of mourning.
Iranian authorities are reported to be on alert to prevent the funeral from turning into a rallying point for reformists. Foreign news media have been forbidden to travel to Qom to cover the funeral.
Ayatollah Montazeri repeatedly accused Iran's leadership of ruling as dictators in the name of Islam, and he spent long periods under house arrest.