BAGHDAD, Iraq – The truck bomb that devastated the U.N. headquarters here was a crude combination of explosives from Saddam Hussein (search)'s old military arsenal, including a giant 500-pound bomb, an FBI investigator said Wednesday. But U.S. and Iraqi officials said it was too early to say who was behind the attack -- Saddam loyalists or foreign terrorists.
The toll stood at 20 killed, including U.N. chief envoy Sergio Vieira de Mello (search), and was expected to climb higher because officials said more bodies were trapped in the rubble of the three-story Canal Hotel.
The hunt for Saddam continued with a raid early Thursday on a farmhouse in the northern town of Abbarah, where an informant told U.S. forces the ousted dictator was hiding. But the tip proved false or late: Soldiers captured five men in the farmhouse, owned by a Saddam loyalist, but Saddam was not among them. The men were being questioned.
In Baghdad, FBI (search) agents searching for clues in the rubble at the U.N. headquarters determined that the bomb was made up of about 1,000 pounds of old ordnance, including mortar rounds, artillery shells, hand grenades and a 500-pound bomb, Special Agent Thomas Fuentes said.
The explosives were piled -- without "any great degree of sophistication or expertise" -- onto the back of a Soviet-made military flatbed truck known as a KAMAZ, not a cement truck as earlier thought, Fuentes said. The vehicle was driven to just outside the concrete wall recently built around the hotel and detonated. Some munitions failed to explode, and investigators and rescue workers had to dig through the site carefully Wednesday to avoid setting them off.
"These munitions were probably in the possession of Iraqi military during Saddam's regime," Fuentes said. "Someone with access to large military cache put them on truck and drove it down an open street." U.S. Army soldiers have turned up plentiful weapons caches across the country in past months.
L. Paul Bremer, the American civil administrator in Iraq, said in a televised interview there are "at least two hypotheses" over the bombing -- one blaming remnants of the Saddam regime, and the other insurgents from neighboring countries. He said more than 100 foreign terrorists were believed to be in Iraq, but did not say which theory seemed more likely at this stage.
Members of Iraq's U.S.-picked Governing Council pointed to Saddam loyalists. After a council meeting Wednesday, 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." He did not elaborate.
Ahmad Chalabi, a prominent council member, warned that the lines between foreign militants and pro-Saddam guerrillas is already blurred, saying Iraqi intelligence reports showed that the Saddam's Fedayeen militia had allied itself with the Al Qaeda-linked Ansar al-Islam (search).
"There is evidence of links between Fedayeen Saddam and Ansar al-Islam," he told a news conference. "Ansar are now in Baghdad and they are compromised of Iraqis from all sects and non-Iraqis."
Chalabi said the Governing Council had received information Aug. 14 that there would be a terror attack in Baghdad using a truck bomb against "a soft target" -- not the U.S. military -- and that the council had warned the United States. Later, his 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."
Bremer said the bombing may have specifically targeted Vieira de Mello, who headed the United Nations' operations in the country. The truck bomb was positioned "quite clearly pretty much in front of de Mello's office, at the back of the U.N. headquarters' building. So it's possible he was, in fact, targeted," Bremer said in a televised interview.
The United Nations began what it called "partial evacuation" by flying 45 staff members -- mostly Westerners -- to Amman, Jordan, U.N. officials in Amman said. The World Bank and the International Monetary Fund, key players in efforts to rebuild Iraq's devastated economy, pulled their staff out of Iraq on Wednesday.
However, a defiant U.N. Secretary-General Kofi Annan vowed that those behind the deadly blast would not succeed in driving the world body out of the country.
"We will persevere. We will continue. It is essential work," Annan told reporters in Stockholm, Sweden, where he stopped on route to U.N. headquarters in New York. "We will not be intimidated."
"We have been in Iraq for 12 years and we have never been attacked," Annan said. He said now the United Nations would reevaluate its security measures.
U.N. operations in Iraq were suspended, and Iraqi employees were told to stay home. Foreign workers were directed to stay in their lodgings that are scattered in many small hotels around the capital.
Unlike U.S. occupation forces, the United Nations had been welcomed by many Iraqis. Bremer said the blast had forced an overall security review, and that coalition officials would meet Friday with all diplomatic missions in Iraq to help them assess security.
Chalabi said the death toll stood at 20 but could go much higher. "There are many who are still trapped in there," he said.
Human remains found in the area where the bomb exploded, about 50 feet from Vieira de Mello's office, suggested a suicide bombing. Fuentes said that could not be absolutely determined until laboratory testing was complete.
The truck bomb was detonated at the concrete wall outside the three-story Canal Hotel at 4:30 p.m. Tuesday, blasting a 6-foot-deep crater in the ground.
The blast ripped through the building as the U.N. Mine Action Coordination Team was giving a press briefing. Television footage captured the head of the team, Solomon Shreuder, speaking to journalists just before the room blacked out and filled with the sound of shattering glass.
Shreuder and the journalists were then seen on tape stumbling out of the darkened room. All survived, officials said.
In Geneva on Wednesday, staff hung a photo of Vieira de Mello on the locked door of his private office in the lakeside headquarters of U.N. High Commissioner for Human Rights, which he heads but left on leave to serve in Iraq. Staff placed flowers and a candle in front of the door next to a pale blue U.N. flag.
In a fresh attack on American forces Wednesday, a soldier was killed and another wounded after they came under small arms fire and crashed into another vehicle while traveling in a convoy near Diwaniyah, 100 miles south of Baghdad, the military said.
Also, insurgents fired a rocket-propelled grenade at a U.S. convoy in Tikrit, killing a civilian working for the occupation force and injuring two soldiers, U.S. Maj. Bryan Luke said.