A string of suicide bombs and attacks against mainly Shia Muslim targets have killed at least 29 people in Iraq.
Three Shia mosques were among the targets
Bombers struck two Shia mosques in Baghdad, killing 16, while three died in an explosion near a Shia procession.
In the evening, a car bomb killed seven people outside a Shia mosque in Iskandariya, south of Baghdad.
The attacks came on the eve of Ashura, the holiest day of the Shia calendar. Three people also died in a suicide bomb in a Sunni area of Baghdad.
That attack took place at an Iraqi police and National Guard checkpoint in the north of the city.
Iraq's borders have been closed and security tightened for Ashura as a result of last year's bomb attacks against Shia worshippers in Baghdad and Karbala that killed at least 181 people.
Friday's violence flared a day after Shia parties were confirmed to have won a slim majority in Iraq's new transitional parliament following January's election.
It could take several weeks of negotiations before a government is formed, as the winning Shia United Iraqi Alliance will have to form a coalition to reach the two-thirds majority needed to pass legislation.
Series of attacks
The deadliest attack took place at a packed Kazimain mosque in southern Doura district at about 1300 (1000 GMT). At least 15 people were killed and several injured when a suicide bomber mingled with worshippers before detonating his explosives.
"I had just begun Friday prayers when an enormous explosion rocked the building," the mosque's imam, Sheikh Malek Kinani told AFP news agency.
SHIA FESTIVAL: ASHURA
Annual Shia festival commemorating martyrdom of Imam Hussein
Hussein, grandson of Prophet Mohammad, killed at Karbala by army of Caliph Yazid in 680
Faithful strike themselves with chains and swords to atone for Hussein martyrdom
The murder 19 years earlier of Ali, Hussein's father, gave rise to the central schism in Islam between Sunni and Shia
At around the same time, two suicide bombers targeted another Shia mosque in western Baghdad. At least one person was killed.
The bombers were accompanied by gunmen who opened fire on guards. But according to the police, the guards fired back and the bombers detonated their explosives.
"I heard someone coming and then he exploded himself," Abdul Qasim Ubid told Reuters television. "There were legs and hands. It was terrible, terrible."
Hours later, a mortar attack struck a cafe in Baghdad, as an Ashura procession passed by. Three people were killed.
Predominantly Sunni Arab militants have vowed to continue targeting Iraq's Shia majority, which is set to take power for the first time.
Ashura marks the death 1,300 years ago of the Prophet Mohammed's grandson, which widened the split between Sunni and Shia Islam.
In other violence, a US soldier was killed and two wounded in a roadside bomb north of Baghdad, the US military said.
It also announced that three US soldiers were killed on Thursday in separate attacks in and around the northern city of Mosul.