Baghdad, Iraq (CNN) -- Twin car bombs exploded near three Iraqi government buildings Sunday in central Baghdad, killing at least 132 people. It was the deadliest attack in the country in more than two years.

More than 500 people were wounded.

The blasts had ripple effects throughout the country, triggering questions about the state of Iraqi security and about national elections planned for January.

No one immediately claimed responsibility.

Iraqi Prime Minister Nuri al-Maliki vowed to punish "the enemies of the Iraqi people who want to spread chaos in the country and derail the political process and prevent the parliamentary elections from taking place as planned."

Surveying the carnage shortly after the explosions, al-Maliki said holding the elections as scheduled would send the strongest response and message to the "enemies of the political process who are supported from the outside."

"The cowardly attack that took place today should not affect the determination of the Iraqi people from continuing their battle against the deposed regime and the gangs of criminal Baath party and the terrorist al Qaeda organization, who have committed the most heinous crimes against the civilians,' " al-Maliki said in a statement.

Iraqi and U.S. officials had warned of a possible increase in violence ahead of the balloting.

President Obama condemned the "outrageous attacks against the Iraqi people." In a statement, Obama called the bombings an attempt to "derail Iraq's progress" and pledged that the United States would be a "close friend and partner" as Iraq prepares for elections.

According to the statement, Obama spoke Sunday with al-Maliki and Iraqi President Jalal Talabani to express his condolences and reiterate U.S. support.

The area struck Sunday is close to the heavily guarded Green Zone that also houses the U.S. Embassy.

Gen. Ray Odierno, the top U.S. military commander in Iraq, and Christopher Hill, U.S. ambassador to Iraq, condemned the bombings, which came a day after the U.S. ambassador to the United Nations, Susan Rice, visited the country for the first time.

"We will assist the Iraqi government in any way we can to ensure that those individuals or groups responsible for such horrific acts be pursued and brought to justice," they said in a joint statement.

The European Union condemned "this terrorist attack" and sent its condolences to the families of the victims, the Swedish presidency said in a statement.

The bombs detonated in quick succession about 10:30 a.m., as the Iraqi work week began, an Interior Ministry official said.

Among more than 500 people wounded were three American security contractors, the U.S. Embassy told CNN. The embassy would not give any more details.

One of the bombs exploded outside Baghdad's governorate building. The other was outside the Justice Ministry, about 500 meters (1,600 feet) away. The nearby Ministry of Municipalities and Public Works also sustained severe damage.

Plumes of smoke billowed from the sites of the attacks as victims fled, some with blood streaming down their faces. The streets were strewn with debris, including charred cars and chunks of concrete from damaged buildings. Some government buildings and others in the area were heavily damaged.

It was the deadliest attack on Iraqi civilians since August 2007, when three truck bombings targeted Iraqi Kurds, killing hundreds in Qahtaniya, in northern Iraq.

In August, more than 100 people were killed in a series of bombings in Baghdad in what Iraqis have dubbed "Bloody Wednesday."

Those attacks shook confidence in the abilities of Iraqi security forces who took over securing urban areas from U.S. troops over the summer. Security was tightened around Baghdad in the wake of the August bombings. Blast walls were erected around the city and more checkpoints were set up.

Susan Rice, the ambassador, completed her two-day visit to Iraq on Saturday that included a condolence stop at the Foreign Ministry, one of the sites attacked in August.

Iraqi journalists grilled officials on TV on Sunday, demanding to know how the most recent attacks could have taken place given the new security measures.

An Iraqi official said the government was working to bolster security, but regional cooperation was needed to help fight suicide bombers.

"We are calling on international and U.N. envoys to come and find out why Iraq is being targeted this way," said Ali al-Dabbagh, the Iraqi government spokesman.

He said Iraq's setbacks are mainly caused by a fledgling intelligence that has "not been completed."

The Iraqi government has blamed Syria for harboring former Baath party members who it said planned the August attacks, and asked for their handover.

Relations between the two neighbors were strained after the bombings. Each withdrew its ambassador from the other's country.

Sunday's bombings came on the day Iraqi officials were due to try to break a logjam holding up a new election law. Iraqis are supposed to go to the polls January 16, but Parliament still has not passed the legislation, putting the balloting in limbo. The original deadline for parliament to pass the law was October 15, because Iraq's electoral commission says it needs 90 days to organize the process.

Iraq's parliament failed Wednesday to reach agreement on a new electoral law, so the issue was supposed go to the Political Council for National Security on Sunday.

CNN's Jomana Karadsheh, Mohammed Jamjoom, and Mohammed Tawfeeq contributed to this report.