Three female suicide bombers killed 28 people and wounded 92 when they blew themselves up among Shi'ites in the streets of Baghdad during a religious pilgrimage on Monday.
There was no immediate claim of responsibility. The Sunni al Qaeda movement often targets Shi'ite pilgrims. It considers Shi'ism - the majority Muslim denomination in Iraq - to be heretical.
At least 1 million people are expected to take part in the pilgrimage, which peaks on Tuesday. It marks the death of one of Shi'ite Islam's 12 imams, one of the most important events in the Shi'ite religious calendar.
In the northern oil city of Kirkuk, a suicide bomber killed 22 people and wounded 150 during a demonstration against a provincial election law.
The attacks were one of the bloodiest days in Iraq in months. Violence has been at its lowest level since early 2004.
Al Qaeda has increasingly used women to carry out suicide attacks because they can often evade more stringent security checks applied to men. The United States military has said women have carried out 20 suicide attacks in Iraq this year.