Two massive suicide car bombings in central Baghdad were "treacherous and despicable acts", Iraq's president has said.
Sunday's blasts, less than a minute apart, left almost 150 people dead and injured more than 700 others.
The attacks targeted the justice ministry and the headquarters of the Baghdad provincial administration close to the Tigris river and near to the high security "Green Zone" in the heart of the Iraqi capital.
In Washington Barack Obama, the US president, condemned what he said were "outrageous" attacks, aimed at derailing progress in Iraq ahead of elections early next year.
Iraq's president, Jalal Talabani, said: "The perpetrators of these treacherous and despicable acts are no longer hiding their objective but to the contrary, they publicly declare that they are targeting the state ... and aiming at blocking the political process, halting it and destroying what we have achieved in the last six years."
At the scene of the blasts, fire engines and ambulances struggled to deal with the massive casualties.
With hundreds of people wounded in the blasts, civilian cars were pressed into service to ferry the injured to area hospitals.
"The walls collapsed and we had to run out," Yasmeen Afdhal, an employee of the Baghdad provincial administration, targeted by one of the bombs, said.
"There are many wounded, and I saw them being taken away. They were pulling victims out of the rubble, and rushing them to ambulances."
Ali al-Dabbagh, an Iraqi government spokesman, said he suspected either al-Qaeda or remnants of Iraq's former government to be behind the attacks.
"The initial analysis shows that it bears the fingerprints of al-Qaeda and the Baathists," he said.
Al-Dabbagh said he was in the nearby al-Mansour hotel when the bombs went off and he and others around him were showered in glass.
The blast came ahead of a planned meeting of Iraqi political leaders to resolve a dispute which could lead to a delay in elections scheduled for January.
Nuri al-Maliki, the Iraqi prime minister, said that if there was a delay "the government ... and parliament will lose its legitimacy, that there would be a return to sectarianism".
Al-Maliki, who later toured the site of the blasts, has also accused al-Qaeda and former Baath party members of being behind the attack.
|The blast ripped the front off the justice ministry building [Reuters]
But Ahmed Rushdi, an Iraqi analyst, said that pointing to al-Qaeda and elements from the Baath Party, the party of Saddam Hussein, the Iraqi leader overthrown in the 2003 US invasion, was an electoral strategy.
"Al-Maliki represents the Dawa party, which is [from] the Shia majority, and we have elections in January. He will say ... 'I'm going to protect you from al-Qaeda and pro-Baathists'," he told Al Jazeera.
"It's always al-Qaeda and pro-Baathist [elements that are blamed]. There is no talking about security infiltration, or the security failures in the Iraqi government."
Mahmoud Othman, a Kurdish MP in the Iraqi parliament, told Al Jazeera the bombing was a message to Iraqi politicians and foreign investors.
"This sends two messages, one of them is to the investment conference in Washington held just a few days ago as if to tell investors not to come to Iraq ... At the same time I think it may be a message to the meeting today of the political council of national security," he said.
"They're trying to solve the problems concerning the elections law. I hope this will urge them to work more than before to solve this problem."
Jalal Talabani, Iraq's president, condemned the attack, as did other world powers.
Barack Obama, the US president, called al-Maliki and Talabani to offer his condolences and pledged to "stand with the Iraqis", the White House said.
Sweden, which currently holds the EU's rotating presidency, said in a statement: "The presidency of the European Union condemns today's car bombs in Baghdad.
"The presidency conveys its condolences to the families of the victims of this terrorist attack."
In August, blasts near government ministries killed almost 100 people and wounded hundreds in Iraq's bloodiest day this year.
Though violence has fallen in Iraq, attacks are still common.
Many Iraqi officials have warned that ahead of the planned elections, violence by groups intent on making the country appear unstable, could rise.