Warning Preceded U.N. Bombing

Iraq's ruling council said today it received warnings of an attack before Tuesday's bombing of the U.N. headquarters in Baghdad, and FBI investigators found evidence the explosive device was packed with military munitions.

FBI agents led the hunt in Iraq today to identify those responsible for detonating an explosives-packed truck outside the U.N. offices. The blast killed at least 20 people, including the U.N. special representative for Iraq, Sergio Vieira de Mello.

Of the more than 100 people who were injured, many were evacuated to hospitals in neighboring Jordan. Rescue work continued today, as officials said people were believed to be still trapped in the rubble of the crumbled building. But with temperatures soaring in the searing Iraqi summer, hopes of finding survivors faded.

Today, as FBI agents began their investigation, Ahmad Chalabi, a prominent member of Iraq's U.S.-picked Governing Council, said the council had received information Aug. 14 that there would be a terror attack in Baghdad using a truck bomb against "a soft target." The council, he said, had warned the United States.

"It [the warning] specifically said that this attack will take place using a truck, to be detonated either using a suicide mechanism or electronic detonation," he said.

Later, Chalabi's Iraqi National Congress issued a statement clarifying his comments, saying it did not warn of an imminent attack on the United Nations and "did not have any specific information related to this criminal act."

Long List of Potential Suspects

No one has claimed responsibility for the bombing, but the list of potential suspects is long. Speaking today on ABCNEWS' Good Morning America , Paul Bremer, the top U.S. civilian administrator in Iraq, said suspects included foreign fighters from countries such as Syria, Sudan and Yemen; forces loyal to ousted dictator Saddam Hussein; and militants from Ansar al-Islam, a group believed to have connections to Osama bin Laden's al Qaeda network.

Members of the Governing Council suspect Saddam loyalists. After a council meeting today, member Mouwafak Al-Rabii told reporters, "There are fingerprints indicating that the act was committed by remnants of the former regime and there are early investigation reports confirming that."

Chalabi said Iraqi intelligence reports showed that Saddam's dreaded Fedayeen militia had allied itself Ansar al-Islam.

"There is evidence of links between Fedayeen Saddam and Ansar al-Islam," he said at a news conference. "Ansar are now in Baghdad and they are compromised of Iraqis from all sects and non-Iraqis."

A ‘Huge and Ambitious’ Explosive Device

An FBI team had already been in Iraq to investigate the Aug. 7 bombing of the Jordanian Embassy in Baghdad. Those agents and technicians turned their attention toward the U.N. attack. They will be joined by more in the coming days.

Investigators in Baghdad focused today on establishing the identity of the owner of the truck, which was driven down an unsecured road running right by the U.N. building in the eastern part of the city to a spot just under Vieira de Mello's office, where it exploded, said FBI Special Agent Thomas Fuentes.

According to Bernard Kerik, the former New York City police commissioner responsible for rebuilding the Iraqi police force, there were "two good witnesses that got a good look at the driver."

FBI agents in Iraq said human remains had been found in the truck, suggesting it was a suicide bombing.

Fuentes described the bomb as a "huge and ambitious device," that weighed as much as 1,500 pounds and consisted of an as-yet-unidentified explosive, packed with loads of Soviet-era mortar shells, grenades, and a 500-pound bomb.

"There's no indication of any of this being homemade," said Fuentes. "This is military, high-explosive munitions."

Fuentes suspected that the munitions were in the Iraqi military's possession during Saddam Hussein's regime. However, he did not place blame for the blast on Saddam loyalists.

Although investigators had not yet completed chemical tests on type of explosives used, Kerik indicated the size of the load was "two to three times the size of the bomb at the Jordanian Embassy." Eleven people died in the bombing of the Jordanian Embassy. No group has claimed responsibility for that attack.

Investigators have identified the truck used in the attack as a 2002 KAMAZ, a large flatbed manufactured in Eastern Europe that was part of the former Iraqi government fleet, ABCNEWS has learned.

Fuentes said investigators have recovered the truck's serial number and license plate. But further tracking efforts have been hindered because Iraqi motor vehicle records were stored on computers that were looted after the war, said Fuentes.

The Finger of Blame

A day after the United Nations suffered its worst attack in history, the organization began a "partial evacuation" of its Baghdad staff to Amman due to raised security concerns, according to a U.N. statement released in the Jordanian capital.

Forty five staff members — mostly Westerners — were flown to Amman, Jordan. The World Bank and the International Monetary Fund, key players in efforts to rebuild Iraq's devastated economy, pulled their staff out of Iraq today.

But the work of the United Nations in Iraq would continue, said U.N. Secretary-General Kofi Annan.

"We will continue our work … We will persevere, we have work to do," he said. "We will not be intimidated."

However, there was some finger-pointing between the United States and the United Nations over who was responsible for the security lapse that led to the bombing.

"The coalition has made some mistakes and maybe we have, too," Annan said, returning to U.N. headquarters in New York after cutting short his summer vacation in Europe. "I don't want to get into finger-pointing, but along the way mistakes have been made by all concerned."

Pentagon officials said U.N. officials rejected some of the procedures the United States wanted to initiate to protect U.N. workers in Iraq.

U.S. troops have maintained a large presence around the scene of the attack in eastern Baghdad, but investigators told ABCNEWS that the United Nations has still not asked for added security from Iraqi police or from coalition forces.

Secretary of State Colin Powell planned to cut short his own vacation to meet with Annan in New York on Thursday.

Some critics have said the United States may have to reconsider its approach and consider bringing in more U.S. troops and involve more countries in its nation-building and peacekeeping mission in Iraq.

However, the United States has no plans to increase military personnel. During a trip to Honduras today, Defense Secretary Donald Rumsfeld said military commanders in Iraq indicated there was no need for more troops. The focus, Rumsfeld said, should be on training Iraqis to provide for their own security.

"At the moment, the conclusion of the responsible military officials [is] that the force levels are where they should be," Rumsfeld said. "The size of the forces in Iraq is appropriate today."

U.N. Community Grieves

If the people behind Tuesday's bombing hoped to win the support of the average Iraqi, they may have picked the wrong target. Some angry Iraqis today condemned the attack.

"This is wrong," one man told ABCNEWS. "The U.N. building belongs to Iraq."

Another man said, "If we don't get rid of those people [terrorists], we won't have stability."

The attack on the Baghdad mission hit the U.N. community especially hard.

Vieira de Mello, a Brazilian diplomat, was one of seven U.N. employees killed in Tuesday's blast. The others were identified as Rick Hooper, an American who worked in the Department of Public Affairs; Fiona Watson, from Britain; Ranillo Buenaventura and Marilyn Manuel, both from the Philippines; Jean-Selim Kanaan, an Egyptian; and Chris Klein-Beckman, a 32-year-old Canadian who worked for the United Nations Children's Fund.

At the world body's headquarters in New York, the blue and white U.N. flag has been lowered to half-staff. A candlelight vigil was held in honor of the dead outside U.N. headquarters tonight.

ABCNEWS' Jim Sciutto, Mike Von Fremd and Tina Babarovic in Baghdad and Bill Greenwood and Martha Raddatz in Washington contributed to this report.