The BBC's Natalia Antelava says security had recently been increased
A series of car bombings has killed at least 127 people and wounded 448 in the centre of the Iraqi capital, Baghdad.
The first blast targeted a police patrol in the Dora district of the city. Four others occurred near official buildings within minutes.
Veteran politician Mowaffaq al-Rubaie, an ex-national security adviser, blamed al-Qaeda militants for the attacks.
He told the BBC their aim was to destabilise the country ahead of general elections due in March.
Natalia Antelava BBC News, Baghdad
All five explosions targeted symbols of this state. Not only ministries but also a university and Baghdad's Institute of Fine Arts.
Officials say that attacks on state-run institutions are designed to undermine the Iraqi government, especially ahead of the parliamentary election, now scheduled for early March. But people here have questions for the authorities too.
Baghdad is lined with blast walls and checkpoints. Officials had said that they had stepped up security. Many here are asking how cars full of explosives continue to get through checkpoints.
"Al-Qaeda has been active in Baghdad recently," Mr Rubaie said.
"The aim is to show the government is unable to protect civilians and its own people and also to deter people from going to ballot boxes."
The Iraqi parliament is holding an emergency session to discuss the bombing. Many MPs have condemned the Iraqi government's handling of the security situation in the capital.
They also condemned the government for failing to provide a senior security minister to answer MPs' questions.
Tuesday's explosions shook houses across the capital.
After the attack in Dora, a bomb blew up in Shourja Market, near the health ministry.
Official buildings located near the other blasts also include the interior ministry, a university and the institute of fine arts.
There were civilian and security force personnel casualties, officials said.
Survivor Ahmed Jabbar, emerging from a damaged ministry building, told the Associated Press news agency: "What crime have we committed? Children and women were buried under debris."
Rescue workers at the scene have been climbing through twisted steel bars and crushed concrete, and dozens of vehicles were burned, AP reported.
Another witness told Reuters news agency: "We were stuck in a heavy traffic jam when a powerful blast took place. A car exploded. A large number of people were wounded and killed."
A spokesman for British Prime Minister Gordon Brown condemned the attacks "in the strongest possible terms".
DEADLIEST ATTACKS SINCE 2003
Aug 2007: More than 500 killed in attacks on villages near Sinjar
Nov 2006: 202 killed in multiple blasts in Baghdad
Apr 2007: 191 killed in car bombings in Baghdad
Mar 2004: 171 killed in bombings in Baghdad and Karbala
Oct 2009: 155 killed in twin truck bomb attacks in Baghdad
Mar 2007: 152 killed in truck bombing in Talafar
Source: News agencies, BBC
"While challenges remain, there have been real improvements in security, the economy and politics in Iraq in recent months and we will continue to work closely with the Iraqi government to continue progress," Mr Brown's spokesman said.
He added: "Those who seek to use violence to undermine these efforts will not succeed."
The US government too condemned the attacks. White House spokesman Robert Gibbs said said the country's leaders who recently passed a new election law were moving Iraq in the right direction, adding: "there are clearly those who are threatened by that".
Iraqi government figures have shown that violence generally has fallen over the past 18 months.
In October, however, co-ordinated bomb attacks killed at least 155 people and wounded hundreds in Baghdad.
Correspondents say that despite occasional massive bombings, insurgents stage frequent smaller-scale attacks against targets such as marketplaces, mosques or schools.
At least eight people - mostly children - died in a school bombing in Baghdad on Monday.
Security has been heightened ahead of the parliamentary elections.
Also on Tuesday, officials set the poll date for 7 March, after initially announcing 6 March as voting day.
No official reason was given for the sudden change, but Kurdish officials said they rejected 6 March - the anniversary of a 1975 treaty with Iran that Kurds say marginalised them.
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