A number of coordinated bombings targeting Iraq's Shiite Muslims killed 72 people Thursday in Baghdad and Nasiriyah.
Authorities said the attacks were similar to those carried out in the past by Sunni insurgents linked to al Qaeda.
The recent attack is an expansion of sectarian violence that exploded in the area just after the last American troops left Iraq in mid-December.
The bombings occurred days before Arbaeen, a Shiite holy day that marks the end of 40 days of mourning after the anniversary of the death of Imam Hussein, a revered Shiite figure.
During this period, Shiite pilgrims from across the country make their way to Karbala, located south of Baghdad.
No group has claimed responsibility for the bombings.
Many in Iraq fear the highly volatile sectarian tensions could reignite Shiite-Sunni warfare, which just a few years ago pushed the country to the brink of civil war.
"People have real fears that the cycle of violence might be revived in this country," Tariq Annad, a 52-year-old government employee, told the Associated Press.