At least 41 people have been killed and 100 injured in a string of attacks in and around the Iraqi capital, Baghdad.
Scores of civilians were injured in the attacks
The targets included a minibus, markets and Iraqi security checkpoints.
The attacks came in defiance of a major security clampdown launched in Baghdad on Wednesday, which has seen thousands of extra troops on the streets.
The bombers seem determined to prove they can continue despite the curfews, checkpoints and combing operations, says the BBC's Jim Muir in Baghdad.
At least nine separate attacks were reported in and around Baghdad. They included car bombs, mortar attacks and a device planted on a minibus.
Baghdad's Haraj and Kazimiya markets were both targeted, causing many civilian casualties.
Security checkpoints in Mahmudiya, a town 30km (20 miles) south of Baghdad, and in Baghdad's Karrada district, were also hit - with many of the casualties reported to be civilians.
Others died when a device devastated a minibus in the al-Amin district of the city.
Since the security clampdown was launched on Wednesday, thousands of extra US and Iraqi troops have been on the streets of Baghdad, manning checkpoints in a high-visibility security operation.
Officials had feared a backlash after the death of the leader of al-Qaeda in Iraq, Abu Musab al-Zarqawi, despite a series of raids targeting his insurgency network in the wake of his death.
But they had also hoped to capitalise on possible disruption to the militants caused by Zarqawi's death and by the subsequent raids, and were keen to be seen as gaining the upper hand over the bombers, correspondents say.
On Friday, a suspected suicide shoe-bomb attack at a key Shia mosque in Baghdad left 11 people dead - an indication that the bombers were prepared to change tactics to beat the new security regime.
In a separate development, the US army said it was hunting for two of its soldiers missing after an attack that killed a third.
The men's checkpoint south of Baghdad came under fire on Friday evening, and when back-up forces got there they found one man dead and two missing, officials said.
Teams of divers are searching canals and rivers near the scene, outside the town of Yusufiya.
"We are currently using every means at our disposal on the ground, in the air and in the water to find them," said US spokesman Major General William Caldwell.
"We... will not stop looking until we find the missing soldiers."