A group of opposition activists went on trial on Saturday in Tehran on charges of rioting and conspiring against the ruling system in connection with protests late last year, Iran's state media reported.

The Human Rights Watch says Iran's post-election unrest is a "full-blown human rights crisis" and calls on Tehran to free government critics detained during the crackdown.

Iran's opposition leader on Friday pledged to remain defiant in the face of new threats - including calls by hard-liners for his execution - and said he was ready to sacrifice his life in defense of the people's right to hold peaceful protests against the government.

Iran's police chief says more than 500 opposition protesters have been arrested since clashes on Sunday that left at least eight dead.

Iranian security forces have limited the movements of a leading opposition figure by refusing to protect him when he leaves his home, his son said Tuesday as authorities broadened their crackdown with a new wave of arrests that included the sister of Nobel peace laureate Shirin Ebadi.