At least 102 people were killed and 200 wounded in a central Baghdad truck bombing today, police sources said.
The blast in al-Sadriya, a Baghdad area where Shia Kurds predominate, sent plumes of black smoke into the air. The area has suffered a number of large bombings in recent months.
The attacker was driving a truck carrying food when he detonated his explosives, destroying shops and stalls that had been set up in the busy outdoor market, police said.
The blast occurred at 4:40pm local time as the market was crowded with people buying food for their evening meal, the latest in a series of attacks against commercial targets in the capital as insurgents seek to maximise the number of people killed ahead of a planned US-Iraqi security sweep.
In the northern city of Kirkuk, the car bombings included a suicide attack, and killed at least four civilians and wounded 37. Two of the cars detonated outside the offices of the main Kurdish parties in the city.
Fearful residents rushed home and shops shut early in anticipation of more attacks, while police imposed a vehicle curfew. A police source said all entrances to Kirkuk were closed to prevent more car bombings.
Further north, another curfew was imposed in Mosul, Iraq's third largest city, after clashes between insurgents and police erupted in several neighbourhoods.
A police source said the militants planned to take over the city. Violence continued despite the curfew. A car bomb hit an ambulance and killed an injured woman who was being taken to hospital and six mortar bombs struck the offices of the state-funded Iraqiya television channel.
In the Shia theological centre of Najaf, Iraq's top Shia cleric Grand Ayatollah Ali al-Sistani repeated his calls for calm. "The Islamic nation is passing through difficult conditions and facing tremendous challenges that threaten its future," his new fatwa, or religious edict, said.
"Everybody knows the necessity for us to stand together and reject the sectarian tension to avoid stirring sectarian differences."
Elsewhere, the US military said two more US soldiers had died in the Sunni province of Anbar, an insurgent stronghold. The military reported the killing of three al-Qaeda militants in a firefight in Falluja and a fourth militant north of Baghdad, and said they belonged to foreign fighter networks.
An Iraqi militant group linked to al-Qaeda earlier vowed to widen its attacks to all parts of Iraq instead of just focusing on Baghdad, after Washington announced plans to beef up its forces in the capital.
The leader of the self-styled Islamic State in Iraq, a body set up by al-Qaeda's Iraq wing and other Sunni militant groups in October, said in a web recording the campaign would stop only "when Bush signs a surrender accord".
"We today announce a strategy ... which is wider and wiser with God's power. It does not involve Baghdad alone but all parts of the Islamic state," said the speaker, identified as Abu Omar al-Baghdadi, leader of the group.
In January Mr Bush said he would send 21,500 more US soldiers to Iraq in an effort to crack down on sectarian killings and insurgent attacks, especially in Baghdad.
Baghdadi said Mr Bush was giving Muslim fighters a chance "to slaughter the wounded crusader giant and take advantage of the collapsing morale of its soldiers and commanders".
The authenticity of the tape could not be verified, but it was posted on web sites used by al-Qaeda and other insurgent groups in Iraq.