Nearly 200 people have been killed in a string of attacks in Iraq's capital, Baghdad - the worst day of violence since a US security operation began.
In one of the deadliest attacks of the last four years, some 140 people were killed in a car bombing in a food market in Sadriya district.
A witness said the area had been turned into "a swimming pool of blood".
The attacks came as PM Nouri Maliki said Iraqi forces would take control of security across Iraq by the year's end.
As the number of people killed in the Sadriya market bombing continued to climb, Mr Maliki called the perpetrators infidels and ordered the detention of the Iraqi army commander responsible for security in that area.
"This monstrous attack today did not distinguish between the old and young, between men and women," he said.
"It targeted the population in a way that reminds us of the massacres and genocide committed by the former dictatorship."
US Defence Secretary Robert Gates said the attacks were "a horrifying thing," but said insurgents would not derail the ongoing security drive in Baghdad.
The bomb in Shia-dominated Sadriya was reportedly left in a parked car and exploded at about 1600 (1200 GMT) in the middle of a crowd of workers and shoppers.
The market was being rebuilt after it was destroyed by a bombing in February which killed more than 130 people.
The powerful bomb started a fire which swept over cars and minibuses parked nearby, burning many people and sending a large plume of smoke over Baghdad.
Sadriya: Car bomb kills 140 at market
Sadr City: Car bomb kills at least 35 at checkpoint
Karrada: Car bomb near private hospital kills at least 11
Al-Shurja: Minibus bomb kills at least two people
Two other attacks kill about 11 more people
Television pictures showed a blasted scene littered with blackened and twisted wreckage.
One witness told the Reuters news agency that many of the victims were women and children.
"I saw dozens of dead bodies," the man said. "Some people were burned alive inside minibuses. Nobody could reach them after the explosion.
"There were pieces of flesh all over the place."
Ahmed Hameed, a shopkeeper in the area said: "The street was transformed into a swimming pool of blood."
About an hour earlier, a suicide car bomb attack on a police checkpoint in Sadr City killed 35 people.
Another parked car bomb killed at least 11 people near a hospital in the Karrada district of Baghdad, while in al-Shurja district at least two people were killed by a bomb left on a minibus.
Two other attacks in the capital killed and wounded about 11 more people.
Hospitals in Baghdad were inundated with more than 200 injured people, many of them with serious burns from the bomb at the Sadriya market.
Car and suicide bombings have occurred almost daily in Baghdad in recent months, despite a US-led security crackdown since February.
The bombers are proving that they can slip through the tightened security net and defy the clampdown, says the BBC's Jim Muir in Baghdad.
Most of the attacks have been in Shia areas, increasing pressure for the Shia militias to step up their campaign of reprisal killings against the Sunni community in which the insurgents are based, says our correspondent.
As Baghdad was rocked by explosions, security in Maysan province to the south was transferred from British to Iraqi control.
6 March 2007: 90 killed in double suicide bombing in Hilla
3 Feb 2007: 130 killed in lorry bomb in a Baghdad market in mainly Shia area
2 Dec 2006: More than 50 killed in car bombs in same Baghdad market
23 Nov 2006: 200 killed in wave of car bombings and mortar blasts in Baghdad's Shia Sadr City
7 April 2006: 85 killed in triple suicide bombing at Shia mosque in Baghdad
Maysan is the fourth of the country's 18 provinces to be handed over to Iraqi security control.
Iraq's national security adviser Mowaffak al-Rubaie said the three provinces of the autonomous Kurdish region would be next.
"Then it will be province by province until we achieve [the complete transfer] before the end of the year," he said in a speech at the handover ceremony delivered on behalf of Prime Minister Maliki.
On Monday, the Iraqi parliament bloc loyal to radical cleric Moqtada Sadr withdrew from the cabinet, demanding Mr Maliki set a timetable for a US troop withdrawal.
But foreign troops are likely to remain in Iraq for some time.
Analysts say that even if Iraqi forces take the lead in providing security across the country, they will need support from US and other coalition troops.
The attacks in Baghdad came as officials from more than 60 countries attended a UN conference in Geneva on the plight of Iraqi refugees.
The UN estimates up to 50,000 people flee the violence in Iraq each month.