A suicide bomber has killed at least 76 people when he slammed his explosives-laden truck into a Kurdish party office in Iraq's northern oil city of Kirkuk.
Two more car bombs exploded nearby, killing a policeman, while another was discovered and safely defused by Iraqi police, according to the US military, which placed the day's death toll at 80 people.
"Local authorities suspect that the first attack was a suicide truck bomb, with the others targeting first responders and Iraqi and coalition security forces," Major Derrick Cheng, a spokesman stationed in Kirkuk, told newswire agency AFP.
The second bomb exploded in a market and wounded a civilian, while another targeted a police patrol, killing an officer and wounding another six people, including five policemen, near the southern edge of town, police said.
The attacks were seen as an attempt to further divide Kirkuk, which ethnic Kurdish leaders want to absorb into their autonomous region in the teeth of furious opposition from Arab and Turkmen residents.
At least 185 bystanders were wounded when the first bomber drove his deadly payload past security barriers next to an office of the Patriotic Union of Kurdistan (PUK), Iraqi President Jalal Talabani's party.
"Most of the wounded, which include women and children, are in critical condition because they are suffering from burns," said Major General Barhan Habib Tayyib, Kirkuk's chief of police.
After the explosion, police cars drove through emptied streets using loudspeakers to urge people to donate blood. Residents thronged outside hospitals, asking about the fate of loved ones.
Witnesses said many nearby buildings had collapsed, and rescue crews scrambled to pull bodies from the wreckage.
Kurdish office targeted
The party office targeted in the first attack housed some local non-governmental organisations, including the city's Olympic committee, and at least two well-known football players and a referee were among the dead.
However, the target was most likely selected as a symbol of Kurdish power.
Since the 2003 US-led invasion ethnically diverse Kirkuk has been seen as a powderkeg, with Arabs, Kurds, and Turkmen divided over the city's political status. But compared to Baghdad it has seen little overt communal fighting.
Before the bombings, US soldiers stationed near Kirkuk spoke of an "acceptable level of violence" — occasional roadside bombs, shootings, and kidnappings, but nothing on the scale of these attacks.
The attack bore the hallmarks of Iraq's Islamist insurgency, which has taken root in the hardscrabble Sunni villages that stretch off to the south-west, where many resent what they see as Kurdish domination.
"The city is a huge oil city, but the Kurds control everything — the security forces, the government, the oil, everything," a Sunni Arab farmer from south of the city told AFP last week, asking not to be named.
Tensions have heightened in recent months because of an article in the Iraqi constitution calling for a referendum by the end of the year to decide whether Kirkuk will join the Kurdish regional government.
The city's Turkmen and Arab communities have demanded that it be postponed until competing land claims resulting from a policy of ethnic cleansing enacted by Saddam Hussein's regime in the 1970s can be settled.
At that time thousands of Kurds were driven from their homes and Arabs from around the country were enticed to move into the region with land grants and cash payouts.
After the regime was toppled in 2003 Kurds streamed back into Kirkuk and now control the local government and much of the security forces.
Two car bombs also went off in Baghdad today, medics and security officials said.
One struck a police patrol in the western Al-Harthiyah neighbourhood, killing three policemen and a civilian. Twenty others, including four policemen, were wounded.
Two women were killed and five people, including three children, were wounded when a parked car exploded in the central Zayuna neighbourhood.
The victims were members of the car owner's family who had returned home after being freed by kidnappers, a security official said.
Police say insurgents often kidnap civilians and booby-trap their vehicles before releasing them in order to set off an explosion later, especially in public places.
Meanwhile, thousands of US and Iraqi troops launched a massive assault on al-Qaeda strongholds south of Baghdad in and around the Sunni town of Jurf al-Sakhr, US military spokeswoman Major Alayne Conway said.