US authorities in Iraq were warned last week that a large-scale terrorist attack on a 'soft' target in Baghdad was being planned.
The warning emerged as rescue teams searched the wreckage of the bombed UN headquarters where at least 20 people, including the senior UN envoy Sergio Vieira de Mello, died in yesterday's suicide truck bombing.
The death toll is expected to rise - some reports said a further four bodies had been found today.
The FBI, which is leading the investigation into the attack, said the bomb was made from 1,000 pounds of old munitions including one single 500 pound bomb, all of the materials from Saddam Hussein's prewar arsenal that required no "great degree of sophistication" to build.
Ahmad Chalabi, a member of the Governing Council and leader of the Iraqi National Congress, said that during a meeting on 14 August "we received information that a large-scale terror attack would take place in Baghdad.
The information said that the attack would be aimed at a soft target, not the American military or forces. The information said the attack would use a truck and would be carried out by using a suicide mechanism or by remote control. We shared this information with the Americans."
FBI Special Agent Thomas Fuentes said that the bomb had been delivered by a KAMAZ flatbed truck, of a kind made in the former Soviet Union.
"We believe it was made from existing military ordnance. I cannot say that it required any great degree of sophistication or expertise to create," Mr Fuentes said.
There was great concern that searchers could be harmed by unexploded materials used in making the bomb, which also consisted of Soviet-era artillery and mortar shells as well as hand grenades.
Earlier UN Secretary-General Kofi Annan said there would be no pull out of Iraq despite the unprecedented attack on its headquarters.
"We will persevere. We will continue. It is essential work," Mr Annan said in Stockholm, where he stopped briefly on his way to UN headquarters in New York. "We will not be intimidated."
Mr Annan said those behind the attack appeared to be organised and sophisticated.
He said there would be a meeting of the Security Council later today to discuss how to provide better protection of UN workers in Iraq following yesterday's attack, when a cement truck packed with explosives detonated outside the Canal Hotel, housing around 300 UN staff.
The explosion blew a 6-foot-deep crater in the ground, ripped apart the building's facade and injured more than 100 people.
Mr Annan, expressing shock at how a UN mission was targeted in the suicide bombing, said:"We are reassessing our security arrangements in Iraq. We have been in Iraq for 12 years and we have never been attacked,"
Mr Annan said Mr de Mello was a "brilliant colleague.The United Nations will continue its humanitarian mission in Iraq so that the victims' deaths shall not be in vain.
UN workers in Iraq were told to stay home today, and some were being evacuated to Jordan.
Mr Annan appeared to indirectly criticize the United States for having underestimated the difficulties of pacifying and rebuilding Iraq following its March invasion to topple Saddam Hussein.
"We had hoped that by now, the coalition forces would have secured the environment for us to be able to carry on ... economic reconstruction and institution building, That has not happened," said Mr Annan, adding that he recognized the difficulty in bringing stability to postwar Iraq.
"Some mistakes may have been made, some wrong assumptions may have been made, but that does not excuse nor justify the kind of senseless violence that we are seeing in Iraq today," he said. "These extremists who are targeting innocent civilians are not doing their nation or the people of Iraq any service."
In another attack on American troops, a civilian working for the occupation forces was killed and two soldiers injured when their convoy was hit by a rocket propelled grenade in Tikrit, northern Iraq.Reuse content