A coordinated wave of car bombings tore through mostly Shia areas of Baghdad, killing at least 66 people and injuring nearly 200.
The bomb attacks took place in markets and other areas frequented by civilians.
These are the latest signs of a rapid deterioration in security in Iraq.
Sectarian tensions have been exacerbated by anti-government protests and the war in neighbouring Syria grinds on.
More than 450 people have been killed across Iraq in May.
Most of the killings came over the past two weeks in the most sustained wave of violence since US troops left in December 2011.
The surge in attacks is reminiscent of the sectarian carnage that pushed Iraq to the brink of civil war in 2006 and 2007.
April was Iraq's deadliest month since June 2008, according to a United Nations tally that put last month's death toll at more than 700.
There was no immediate claim of responsibility for today's bombings, but they bore the hallmarks of al-Qaeda's Iraqi arm.
The group, known as the Islamic State of Iraq, frequently uses car bombs and coordinated blasts against Shias to undermine Iraqis' confidence in the Shia-led government.
The day's deadliest attack happened when two bombs exploded in the eastern Habibiya area on the edge of the sprawling Shia district of Sadr City.
Those blasts killed 12 and wounded 35, police said.
Twin blasts also struck an open-air market in the predominantly Shia al-Maalif area, killing six and wounding 12.
Another car bomb exploded in the busy commercial Sadoun Street in downtown Baghdad.
It killed five civilians and wounded 14, police said.
Among the injured were four policemen who were at a nearby checkpoint.
The central street is one of the capital's main commercial areas and is lined with clinics, pharmacies and shops.
Firefighters were seen struggling to extinguish flames as police sealed off the area.
Several shops were partially damaged or burned.
Elsewhere across the bloodied capital city, police reported that a car bomb went off in the eastern New Baghdad area as officers were waiting for explosives experts to dismantle it.
A civilian was killed and nine others injured.
In the north, a blast in the Sabi al-Boor neighborhood killed eight civilians and injured 26.
In the Kazimiyah district, a car bomb blew up near a bus and taxi stop, killing four and wounding 11.
Another blast killed four and wounded nine in the Shaab area.
An attack in the Hurriyah neighbourhood left five dead and 14 injured.
A bomb in the southwestern neighbourhood of Bayaa killed six civilians and injured 16.
In Baghdad's central Sadria area, a car bomb killed three civilians and injured 11.
In the east, a blast killed five and injured 12 in the Jisr Diyala area. Car bombs also struck the Baladiyat neighbourhood, killing four and injuring 11.
In Madain, about 20km (12 miles) south of central Baghdad, a car bomb killed three and injured nine.
The day's bloodshed was the deadliest since last Monday, when a wave of attacks killed 113 people in Shia and Sunni areas.
