In the deadliest blast, at least 15 worshippers died when a suicide bomber struck at prayer time. At the same time, suicide attackers struck another mosque, killing one person, while at least two people died in a blast at a Baghdad cafe. The attacks came on the eve of Ashura, the holiest day of the Shia calendar. It follows a period of relative calm in Iraq after regular insurgent attacks.
In the first attack, a bomber mingled with worshippers at the packed mosque in southern Doura district before triggering the blast at about 1300 local time (1000 GMT). "The attack was carried out by a suicide bomber wearing an explosives belt at the Kazimain mosque in Abu Dishr near Doura," a police officer told AFP news agency. Ahmed Zaher, a doctor at Baghdad's al-Yarmuk hospital, told AP news agency casualties were being brought in in cars and pick-up trucks.
At around the same time as the attack in Doura, two suicide bombers targeted another Shia mosque in western Baghdad, police said. The bombers were accompanied by gunmen who opened fire on guards at the mosque. But according to the police, the guards fired back and the bombers detonated their explosives.
Abdul Qasim Ubid told Reuters television he saw the attackers strike. "I heard someone coming and then he exploded himself. There were legs and hands. It was terrible, terrible," he said. One person was killed and four others injured, police and hospital sources said.
Hours later, attackers targeted a cafe in Baghdad, as an Ashura procession passed by. The BBC's Jon Leyne in Baghdad says the blast, caused by a suicide attack or a mortar, killed the cafe's owner and a relative and possibly one other person.
Iraqi security forces have increased security for Ashura to try to avoid a repeat of last year's bomb attacks against Shia worshippers in Baghdad and Karbala that killed at least 181 people. Iraq's land borders have been closed until Tuesday.
Predominantly Sunni Muslim militants have vowed to continue targeting Iraq's Shia majority, which is set to take power for the first time in the country's history. Ashura marks the death 1,300 years ago of the Prophet Mohammed's grandson, which widened the split between Sunni and Shia Islam