Iraqi officials say bombs targeting security forces and Shi'ite pilgrims have killed at least 22 people.
The deadliest attack Wednesday happened near the northern city of Tikrit where a suicide bomber blew up a vehicle at a police checkpoint. The blast killed at least 10 people, including two policemen.
In Baqouba, north of the capital, Baghdad, three coordinated blasts struck a group of Shi'ites observing the annual mourning period known as Ashura, killing at least eight people and wounding 10 others.
Another bomb targeting police near the former insurgent stronghold of Fallujah killed four people.
The Ashura ritual commemorates the seventh-century killing of Imam Hussein, a grandson of the Prophet Muhammad, during a battle with rival Muslims.
There was no immediate claim of responsibility for the attack, but Sunni Muslim extremists often target Shi'ites participating in religious events.
A Shi'ite worshipper beats himself with chains as a sign of grief for Imam Hussein during Muharram between the holy shrines of Imam Hussein and Imam Abbas in Karbala, Iraq, Nov. 13, 2013.
Supporters of Iraq's largest Shi'ite party, the Supreme Islamic Iraqi Council, listen to their leader, Ammar al-Hakim, during a rally to mark Muharram, Baghdad, Nov. 13, 2013.
Shi'ite worshippers gather between the holy shrines of Imam Hussein and Imam Abbas, seen in the background, during Muharram in Karbala, Iraq, Nov. 12, 2013.
Shi'ite worshippers gather between the holy shrines of Imam Hussein and Imam Abbas during Muharram in Karbala, Iraq, Nov. 12, 2013.
Shi'ite worshippers enter the holy shrine of Imam Abbas, brother of Imam Hussein, during Muharram in Karbala, Iraq, Nov. 12, 2013.
A Shi'ite Muslim man gashes his forehead with a sword before the religious festival of Ashura in Najaf, Iraq, Nov. 11, 2013.
Shi'ite pilgrims beat themselves with iron chains as they take part in the Ashura procession in Karbala, Iraq, Nov. 11, 2013.