(CNN) -- U.S. President Obama and German Chancellor Angela Merkel on Monday condemned this week's violent crackdown on pro-democracy protesters in Iran.
In separate statements, the two Western leaders called on Iran to abide by international obligations to respect the rights of the Iranian people to demonstrate for political change.
Iran's Supreme National Security Council said eight people were killed in the latest series of clashes over the weekend, making the unrest the deadliest since June.
"The United States joins with the international community in strongly condemning the violent and unjust suppression of innocent Iranian citizens, which has apparently resulted in detentions, injuries, and even death," Obama told journalists in a break from his Christmas holiday in Hawaii.
The latest fighting came on the anniversary of Ashura, a major Shiite Muslim holy day marking the death of Imam Hussein, grandson of Prophet Mohammed, as a martyr. Large crowds pour into streets each year for the observance.
"For months, the Iranian people have sought nothing more than to exercise their universal rights," Obama said. "Each time they have done so, they have been met with the iron fist of brutality, even on solemn occasions and holy days."
Obama rejected past claims by Iranian leaders that the violence is fomented by the United States and other foreign influences.
"It's about the Iranian people and their aspirations for justice and a better life for themselves," Obama said. "And the decision of Iran's leaders to govern through fear and tyranny will not succeed in making those aspirations go away."
In particular, Obama said, the United States called on Iran to abide by international obligations to respect the rights of its own people, and to release "all who have been unjustly detained within Iran."
Merkel's statement said she condemned the latest clashes "where the unacceptable behavior of the security forces has led to the deaths of people."
"I call on Iran to stand by its commitments under the 'International Pact for Human and Civil Rights,' " Merkel said in her statement. "In particular the right to free speech and freedom of assembly may not be infringed upon. We are calling on officials to prevent an escalation of the situation and to make room for dialogue with the opposition in contested topics."
Both the United States and Germany have been part of negotiations intended to prevent Iran from developing nuclear weapons.
In Washington, U.S. State Department spokesman Ian Kelly said the United States was willing to engage with Iran "to try and allay our concerns about the peaceful nature of their nuclear program, and at the same time, we of course are going to speak out in support of those who are out there trying to exercise their democratic rights."