As sectarian violence flared, authorities placed security forces on high alert and extended curfew hours in Baghdad and several other cities.
Police say they have found dozens of bodies killed overnight in and around Baghdad. The bodies of 47 people shot to death were found in one village southeast of the capital.
Three journalists working for the Dubai-based Al Arabiya television network were killed near Samarra.
In the southern city of Basra, gunmen dressed in police uniforms raided a prison and killed 11 Sunni detainees, including several foreign militants.
Shi'ites dominate Iraq's police force.
A major Sunni political alliance, the Iraqi Accordance Front, says the government must apologize for the reprisal attacks. The alliance says it will not attend a multi-party meeting President Jalal Talabani has called to discuss the situation, and will boycott talks on forming the next government
Separately, at least 12 people, including eight Iraqi soldiers, were killed in a roadside bomb blast Thursday in Baquba, northeast of Baghdad.
The violence flared despite calls for calm from top government officials and senior clerics
The Askariya shrine draws pilgrims from around the world. It contains the tombs of the 10th and 11th Shi'ite imams, Ali al-Hadi and his son, Hassan al-Askari, who died in 874. The shrine was built at the site where the 12th Shi'ite imam, Mohammed al-Mahdi, disappeared. He is called the hidden imam and is the son and grandson of the two imams buried at Askariya.
Some information for this report was provided by AFP, AP and Reuters.