The United States strongly condemned the violence in Iran, offering its support to those who seek universal rights.
National Security Council spokesman Mike Hammer on Sunday denounced Teheran's "unjust suppression of civilians" in a crackdown that has killed at least four people, including the nephew of an opposition leader. Hammer says governing through fear and violence is not just.
Hammer quoted President Barack Obama's Nobel Peace Prize acceptance speech, saying "it is telling when governments fear the aspirations of their own people more than the power of any other nation."
Witnesses and opposition Web sites said Iranian security forces on Sunday engaged in the fiercest clashes with anti-government protesters in months.