Bombings and a mortar attack struck Shiite targets in Baghdad and north of the Iraqi capital today, killing as many as 100 people and wounding many more.
The bombs exploded in a crowded market for second-hand goods at around noon local time, and followed a bloody weekend in the capital which included 12 US soldiers dying in a helicopter crash today blamed on insurgent rocket fire.
In all, 25 of 27 servicemen killed at the weekend, died on Saturday making it the third deadliest day for US troops since the war started in March 2003.
Today's attacks coincided with the imminent arrival of 21,500 US troops in Iraq ahead of a new offensive against insurgents recently announced by President George W Bush.
Some 17,000 troops are due to be deployed in Baghdad, where US generals say previous offensives failed because there were too few troops on the ground to hold neighbourhoods cleared in house-to-house sweeps.
Today's first blast, a parked car bomb, tore through stalls of vendors in the Bab al-Sharji area - one of the busiest parts of Baghdad.
Seconds later, a suicide car bomber drove into the crowd. Police estimated that each car was loaded with nearly 220 pounds of explosives.
There were conflicting reports about the casualty toll as the wounded were rushed to several hospitals around the capital.
Deputy Health Minister Hakim al-Zamili said at least 78 people were killed and 156 were wounded, making it the deadliest attack in two months, but figures provided by police and hospital officials showed that as many as 88 people were killed.
The explosions left body parts strewn on the bloodstained pavement as black smoke rose into the sky. Police sealed off the area as ambulances rushed to the scene.
Survivors were taken to nearby al-Kindi Hospital where emergency personnel worked feverishly over the bloodied and badly wounded.
A suicide bomber killed at least 63 people in the same area last month.
Prime Minister Nouri Maliki, a Shiite, denounced the attack. "We condemn this crime and we promise that the security forces will pursue all those involved in this crime and bring them to justice," he said in a statement.
Hours later a bomb followed by a mortar attack struck a market in the predominantly Shiite town of Khalis, 50 miles north of Baghdad, killing at least 12 people and wounding 29, police said.
In other violence, gunmen killed a teacher as she was on her way to work at a girls' school in the mainly Sunni area of Khadra in western Baghdad.
Two mortar shells also landed on a primary school in the Sunni stronghold neighbourhood of Dora in southern Baghdad, killing one woman waiting for her child and wounding eight students.
Police also said that a phone company employee and a Sunni tribal chieftain were killed in separate shootings in Baghdad, while the bullet-riddled bodies of three men were found elsewhere in the capital.
An oil technician also was shot to death in the northern city of Mosul.
Meanwhile, the US military helicopter that crashed outside Baghdad on Saturday, killing all 12 on board, was shot down by hostile fire, CNN reported today.
It said military sources had indicated the Black Hawk was most likely brought down by a shoulder-fired missile.
The crash was still under investigation but debris recovered on the ground indicate a missile was involved, CNN said.