Coordinated suicide bombings in the Iraqi capital Baghdad and the city of Karbala have killed 170 people who were marking Ashura -- one of the most solemn days of the year for Shi'ite Muslims.
Officials in Baghdad say three suicide bombers killed 58 people near the city's Kazamiya shrine. A fourth bomber was reportedly arrested.
Further south, in the Shi'ite holy city of Karbala, a combination of suicide bombers, remote-controlled devices and mortar fire killed 112 people as more than one million gathered for ceremonies around the Imam Hussein shrine and the Abbas mosque.
More than 400 people were injured in the two attacks.
Shi'ite Muslims from around the world had traveled to Iraq to commemorate the death in battle of Imam Hussein, a grandson of the prophet Mohammed, more than 13-hundred years ago. Iran's interior ministry said 40 or 50 Iranians were among those killed or wounded in Tuesday's attacks. Iraq's Governing Council condemned the attacks as an attempt to cause divisions among the Iraqi people, and announced three days of national mourning.
The top Shi'ite cleric in Iraq, Ayatollah Ali al-Sistani, and a Shi'ite member of the Governing Council, Abdel Aziz al-Hakim, blamed US security policies for the attacks. They say the United States, as an occupying power, is responsible for ensuring security.
US administrator Paul Bremer vowed to bring those behind the blasts to justice. The White House also strongly condemned the attacks, saying the perpetrators are enemies of freedom in Iraq.
US-led coalition authorities have long been concerned about the possibility of insurgent attacks during Ashura observances, which were banned in Iraq for decades under Saddam Hussein.
There were no immediate claims of responsibility, but US and Iraqi officials noted that a letter intercepted last month by an al-Qaida terrorist suspect called for suicide bombings against Shi'ites to provoke civil war in Iraq.