BBC News
More than 150 people have been killed and hundreds injured in a series of bomb attacks and shootings across Iraq.
In the worst incident, at least 114 people were killed and 160 injured when a car bomb exploded in Baghdad's mainly Shia district of Kadhimiya.
During the night, gunmen killed 17 people in the nearby town of Taji after dragging them from their homes.
Al-Qaeda in Iraq claimed it had begun a nationwide bombing campaign to avenge a recent major offensive on rebels.
In a statement on a website, the group said it acted after US and Iraqi forces attacked insurgents in the northern town of Talafar.
Iraqi officials said 157 rebels were killed and nearly 300 arrested during the operation.
Wednesday became one of the deadliest days in Iraq since the US-led invasion in March 2003.
The attacks once again showed the limits of military might as a solution to the insurgency, the BBC's Rob Watson says.
When under military pressure in one part of Iraq, the insurgents simply strike elsewhere, our defence and security correspondent says.
The attacks came as a final draft of the Iraqi constitution was handed to the UN.
After months of negotiations, the draft is due to be distributed to Iraqis before a referendum on it on 15 October.
In attacks elsewhere:
Three Iraqi soldiers are killed when a car bomb targets their patrol in the Al-Adel district of western Baghdad
* A bomb explodes by an Iraqi National Guard convoy in the northern Baghdad district of Shula, killing at least four people and wounding 22
* Two US soldiers are wounded as a suicide bomber rams a vehicle packed with explosives into their Humvee in east Baghdad
* Gunmen kill four policemen in Baghdad's northern district of Adhamiya. Three Iraqi soldiers and four policemen die when a suicide car bomber strikes as rescuers arrive to help
* A suicide car bomber attacks a US convoy close to the Rashid Hotel in the Green Zone, although it is not yet known if there were any other casualties
* A suicide bomber blows himself up in Baghdad without causing any other casualties.
Labourers targeted
A suicide bomber drove his car at 0630 (0230 GMT) into queues of labourers who had gathered on Oruba Square in Kadhimiya, Iraqi police spokesman Maj Musa Abdel Kerim said.
Every day, large numbers of construction workers gather in the square in the north of the city to be picked up by their employers.
According to some reports the attacker lured the workers towards the vehicle before detonating the bomb.
"We gathered and suddenly a car blew up and turned the area into fire and dust and darkness," one of the workers, a man named Hadi, told Reuters news agency.
British Foreign Office Minister Kim Howells said in Baghdad that the latest attacks "will not stop the heroic attempts of the Iraqi people to create a safe, brighter future".
There have been frequent sectarian killings in Baghdad and central Iraq as mainly Sunni insurgents seek to incite fear and hatred between the Muslim communities.
