At least 42 people have been killed and dozens more wounded after a string of bombings across Iraq, many in Shia-majority cities.
The attacks are a grim reminder of the government's failure to stem the upsurge in violence that is feeding sectarian tensions across the country.
The Sunni militant group and other Sunni extremists often targets Shia civilians in an effort to undermine the Shia-led government. Al Qaida's extremist ideology considers Shias heretics.
The deadliest of Sunday's attacks, many of which struck busy commercial areas, happened in the southern city of Hillah, 60 miles south of Baghdad. Back-to-back car bombings hit an outdoor market there, killing eight people and wounding 22, police said.
Two parked car bombs ripped through a commercial area in the city of Suwayrah, 25 miles south of Baghdad, killing five people and wounding 14. Two other car bombs exploded simultaneously in the city of Kut, 100 miles south-east of Baghdad, killing four and wounding 16, according to police.
In the nearby city of Samawah, 230 miles south-east of Baghdad, four people were killed and 13 wounded when two car bombs exploded. Two other car bombs killed three and wounded 13 in the city of Diwaniyah, 80 miles south of the capital.
Samarra was struck twice on Sunday, a day after a car bombing in the Sunni-dominated city left 17 dead. The memory of the 2006 bombing of the city's al-Askari Shia shrine still haunts many Iraqis because it set off years of retaliatory bloodshed between Sunni and Shia extremists.
Two people were killed and 15 were wounded in the morning when a car bomb exploded near a group of mourners at a funeral for some of the previous day's dead.
A suicide bomber struck a security checkpoint near the shrine in the Sunni-dominated city later in the day, killing four and wounding 10, said Mizhar Fleih, the deputy head of the municipal council there.
In other violence on Sunday, police reported five people killed and 34 wounded in the southern city of Basra and the central towns of Mahmoudiyah and Madain.
In the western Baghdad neighbourhood of Sadiyah, police said a bomb went off near a row of shops, killing two people and wounding nine others.
Three others were killed in a blast near a soccer field in Baghdad's mainly Shia south-eastern suburb of Nahrwan. Yet another bomb exploded in the western Amariyah neighbourhood, killing two and wounding 10, police said.
More than 5,000 people have been killed in Iraq since attacks began accelerating in April following a deadly security crackdown against a Sunni protest camp in the northern town of Hawija.
Including today's death toll, at least 267 people have been killed so far in October. The latest surge in violence has raised fears that Iraq could be returning to widespread sectarian killings similar to those that brought country to the edge of civil war in 2006 and 2007.