WASHINGTON - Three years before the September 11 attacks, US intelligence agencies had information that a group planned to fly an explosives-laden plane from a foreign country in the World Trade Centre.

A US congressional hearing was told the information, obtained in August 1998 about the group of "unidentified Arabs", was passed to the FBI and the Federal Aviation Administration. However, "the FAA found the plot highly unlikely given the state of that foreign country's aviation programme," said Eleanor Hill, staff director of the joint Sept. 11 inquiry of the House and Senate intelligence committees.

This was one of many details revealed at the first public hearing into intelligence failures by America's spy agencies to detect plans by Osama bin Laden and his al Qaeda network.

While most of the rising volume of threat reports about an impending attack during spring and summer of 2001 pointed to a strike overseas, some of it suggested targets inside the United States, Hill told the hearing.

But none of the threats provided a specific time, date, and place of the attack. "My own view is ... no one will ever really know whether 9/11 could have been prevented," she said.

On September 11, four hijacked planes crashed into the World Trade Centre in New York, the Pentagon near Washington and a Pennsylvania field, killing about 3,000 people. The United States blames bin Laden and his al Qaeda network.

Despite concerns about bin Laden and al Qaeda, intelligence agencies had not directed adequate resources to analyzing them, Hill said.

Before the September 11 attacks, the CIA's Counterterrorist Centre had only five analysts assigned full-time to bin Laden's network worldwide, and the FBI's terrorism analytic unit had only one analyst looking at al Qaeda long-term, she said.

A senior CIA official said there had been 125 analysts throughout the agency focused on tracking bin Laden and al Qaeda, not just the ones in the Counterterrorist Centre's small bin Laden unit.

In March 2001 an intelligence source claimed a group of bin Laden's operatives were planning an attack in the United States in April 2001. That April, information was obtained that "unspecified terrorist operatives" in California and New York were planning terrorist attacks in those states, Hill said.

In May 2001 intelligence agencies had information that bin Laden supporters were planning to infiltrate the United States through Canada to conduct an attack using explosives.

In the same month, the Defense Department acquired information that it shared with other intelligence agencies indicating that seven bin Laden associates had departed various locations for Canada, Britain and the United States.

In June 2001, Hill said, CIA's counterterrorist Centre had information that key operatives in bin Laden's organisation "were disappearing while others were preparing for martyrdom."

The National Security Agency, which eavesdrops on global communications, reported at least 33 communications between May and July 2001 indicating a "possible, imminent terrorist attack," she said.

"This is not an example of missed signals, this is an example of how many signals there are out there," the CIA official said. "It illustrates how much information is coming in, how difficult it is to sort out, specifically when it's not specific," he said.

There were also threat reports that terrorists were considering using airplanes as weapons as a method of attack.

In August 2001, a month before the attacks, intelligence agencies had information about a plot to either bomb the US Embassy in Nairobi from an airplane or crash an airplane into it, Hill said.

In April 2001, a source said that bin Laden would be interested in commercial pilots as potential terrorists.

A year earlier, in April 2000, a source walked into the FBI's Newark office and claimed he had been to an al Qaeda training camp in Pakistan where he learned hijacking techniques and received arms training. He said he was supposed to meet five to six others in the United States to hijack a jumbo jet.

"They were instructed to use all necessary force to take over the plane because there would be pilots among the hijacking team," Hill said. The source passed a polygraph but the FBI was not able to verify his story, she said.

US intelligence agencies had known about a rising al Qaeda leader since 1995 but had not recognised his growing importance in bin Laden's network until recently, Hill said.

She did not name him, but sources told Reuters that Hill was referring to Khaled Sheikh Mohammad, who officials now say could fill the leadership gap if bin Laden died, and who was instrumental in planning the September 11 attacks.

"Prior to September 11, 2001, there was little analytic focus given to him and coordination among the intelligence agencies was irregular at best," Hill said.

CIA Director George Tenet declined to declassify the al Qaeda leader's identity and information about him, she said. The issue was important to the inquiry, Hill added.

"We now know that our inability to detect and prevent the Sept. 11 attacks was an intelligence failure of unprecedented magnitude," Senator Richard Shelby of Alabama, the senior Republican on the Senate intelligence committee, said. "Some people who couldn't seem to utter the words 'intelligence failure' are now convinced of it."

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