Iraqi officials said at least 155 people were killed and 540 others wounded when twin car bombs that appeared to target government buildings in downtown Baghdad during rush hour exploded, marking the country's deadliest attack in two years.

The powerful blasts went off less than a minute apart Sunday in parking lots near the headquarters of the Baghdad provincial administration and the Ministry of Justice building.

VIDEO: Baghdad Blasts

There were so many wounded that even civilian cars were pressed into service to bring the casualties to area hospitals.

SLIDESHOW: Baghdad Bombings (Warning: Graphic)

"I strongly condemn these outrageous attacks on the Iraqi people, and send my deepest condolences to those who have lost loved ones," said President Obama in a statement released Sunday.

"These bombings serve no purpose other than the murder of innocent men, women and children, and they only reveal the hateful and destructive agenda of those who would deny the Iraqi people the future that they deserve. These attempts to derail Iraq's progress are no match for the courage and resilience of the Iraqi people, and their determination to build strong institutions."

Obama said the U.S. remains committed to stand with Iraqis and help them "build greater peace and opportunity."

Secretary Hillary Clinton expressed her condolences: "I want to personally express my heartfelt condolences to the victims of today's savage attacks in Baghdad and for the tragic loss of so many Iraqi lives. I strongly condemn the bombings at the Iraqi Ministry of Justice and the headquarters of the Baghdad Provincial Administration."

"These despicable terrorist attacks seek to undermine the impressive progress that Iraq has made towards stability and self-reliance. They will not succeed. They will not deter Iraqis from administering justice based on the rule of law and carrying out their legitimate responsibilities in governing Baghdad," said Clinton.

In a joint statement released Sunday, Ambassadors Christoper Hill and General Ray Odierno condemned the Baghdad bombings.

"These despicable terrorist attacks serve no legitimate purpose. They will not deter Iraqis from administering justice based on the rule of law and carrying out their legitimate responsibilities in governing Baghdad. At this crucial time leading up to national elections, we call upon all Iraqis to work together to combat all forms of violence and attempts at intimidation," the ambassadors said.

They promised to work with the Iraqi government to make sure that those responsible for the bombings are "pursed and brought to justice in accordance with Iraqi law."

"We will continue to support the people and government of Iraq in fighting terrorism. We mourn the senseless loss of life and extend our condolences to the victims' families, friends, and community."

While violence has dropped dramatically in the country since the height of the sectarian tensions, such bombings like Sunday's demonstrate the precarious nature of the security gains and the insurgency's abilities to still pull off devastating attacks in the heart of what is supposed to be one of Baghdad's most secure areas.

In August, coordinated blasts against two ministries killed more than 100 people.

Sunday's explosions went off less than a minute apart near two prominent government institutions — the Ministry of Justice and the headquarters of the Baghdad provincial administration — in a neighborhood that houses a number of government institutions such as the Ministry of Labor.

The area is just a few hundred yards from the heavily protected Green Zone that houses the U.S. Embassy as well as the offices of Prime Minister Nouri al-Maliki.

An official with the U.S. Embassy in Baghdad said two American security contractors were injured in the blast, but could not provide details about who they worked for, including whether they were associated with the Embassy, or the nature of their injuries.

The official spoke on condition of anonymity because she was not authorized to release the information.

U.S. security contractors could be seen at the site of the explosions helping the wounded.

Iraqi police and Interior Ministry officials, speaking on condition of anonymity because they were not authorized to speak to the media, gave the death toll.

The explosions were caused by car bombs aimed at government institutions, said Maj. Gen. Qassim al-Mousawi, spokesman for the city's operations command center. He added that it was not known whether they were homicide attacks.

"They are targeting the government and the political process in the country," al-Mousawi told The Associated Press.

Yasmeen Afdhal, a 24-year-old employee at the Baghdad provincial administration, said that after the first blast, dozens of employees began fleeing the building.

"The walls collapsed and we had to run out," said Afdhal, who was not injured in the explosion. "There are many wounded, and I saw them being taken away. They were taking victims out of the rubble, and rushing them to ambulances."

Black smoke could be seen billowing from the area where the blasts occurred, as emergency service vehicles sped to the scene. Even civilian cars were being used to transport the wounded to hospitals, al-Mousawi said.

A Shiite member of the Baghdad Provincial Council, Mohammed al-Rubaiey, said at least 25 members of the provincial council staff were killed in the blasts and that the wounded were still being taken to the hospital.

"This is a political struggle, the price of which we are paying," he said. "Every politician is responsible and even the government is responsible, as well as security leaders."

The explosions were just a few hundred yards from Iraq's Foreign Ministry which is still rebuilding after massive bombings there in August killed about 100 people. The bombings were a devastating blow for a country that has seen a dramatic drop in violence since the height of the sectarian tensions in 2006 and 2007.

Such attacks near prominent government institutions come as Iraq is preparing for January elections.

The Associated Press contributed to this report.