Just a few weeks ago, they would have been virtually unthinkable acts of defiance in Iran: standing up to the supreme leader, ignoring his warnings to stay off the streets — then chanting for his death.

But the boisterous opposition protests thrusting Iran into its worst civil unrest since the 1979 Islamic Revolution have broken the taboo against direct criticism of Ayatollah Ali Khamenei. Now some are talking about him as a casualty of the crisis — and wondering if the aloof cleric''s powerful office will survive after his eventual death.

For two decades, Khamenei''s word has been law in Iran, where the supreme leader is considered God''s representative on Earth. Today he is reviled, not revered, by thousands of supporters of opposition leader Mir Hossein Mousavi, who claims he was defrauded in the June 12 presidential elections.

Unprecedented chants of "Death to Khamenei!" by some protesters underscore an astonishing blow to the 70-year-old cleric''s standing.

"The election dispute may further erode his religious and political authority, especially among the traditional clergy, leaving him even more dependent on the Revolutionary Guard," Iran''s most powerful and feared security force, said Ali Nader, an Iran expert with the RAND Corp.