A car bomb exploded in a busy market in northeastern Iraq on Thursday, killing at least 25 people and wounding more than 30, the town's mayor and medical sources said.
Iraq is suffering its worst wave of violence in at least five years, with insurgents targeting mainly Shi'ite Muslim civilians in attacks on public places such as shopping areas and cafes.
The attack took place in Sadiya, 65 km (40 miles) northeast of Baghdad.
"I was sitting in my store when I heard a huge explosion. I could not recognise anything because dust engulfed the place. Shattered glass was everywhere," grocery store owner Suhair Gadhban told Reuters by telephone, adding that he was wounded in the leg.
Suhair said he saw dozens of people lying near the scene of the explosion as he was being taken for medical aid.
"Some of them had been killed and others were seriously wounded and were screaming for help," he said.
Later in the day, three bombs exploded in Baghdad's western Amiriya district, killing seven people and wounding 18, police said. The capital has been hit by almost daily attacks since the start of the year.
The son of a police officer was also killed in the north of the city when a bomb attached to his car exploded.
Some 20 km (12 miles) north of Baghdad a suicide bomber detonated himself at a police checkpoint in Taji, killing four police officers and wounding eight. Two people were also killed in the northern city of Mosul in roadside explosions, police said. Altogether 39 people were killed in Iraq on Thursday.
Hundreds of Iraqis have been killed every month in 2013, and the frequency and severity of bomb attacks has raised fears that Iraq could descend once more into the kind of sectarian bloodshed of 2006-2007, when tens of thousands died.
Nearly two years since U.S. troops withdrew from Iraq, security forces are struggling to combat the violence. Insurgents, some linked to al Qaeda, have also benefited from the civil war in neighbouring Syria.