The White House Sunday condemned the Iranian government's "unjust suppression" of civilians after it was reported at least five were killed in street protests.
Allegedly among the dead is the nephew of opposition leader Mir Hossein Mousavi, the Associated Press reported.
"We strongly condemn the violent and unjust suppression of civilians in Iran seeking to exercise their universal rights," National Security Council spokesman Mike Hammer said in a statement. "Hope and history are on the side of those who peacefully seek their universal rights, and so is the United States."
According to state police, several were arrested and 300 were injured during the protests. Police deny firing guns during the dispute.
Since the disputed presidential elections in June, protesters have held frequent protests against President Mahmoud Ahmadinejad who was declared the winner over Mousavi.
The protests are coinciding with the Shiite holy day of Ashura.
"Governing through fear and violence is never just, and as President Obama said in Oslo - it is telling when governments fear the aspirations of their own people more than the power of any other nation," added Hammer.