CIA operatives foiled two attacks on US embassies last year in advanced stages of planning and disrupted three other plots after infiltrating terrorist cells and by monitoring and intercepting electronic communications, administration and congressional sources said on Monday.
In the wake of twin terrorist bombings of US embassies last week in Kenya and Tanzania, the sources refused to provide details about the locations of the intended targets of the 1997 attacks, or how they were uncovered, for fear of tipping off terrorists to US intelligence gathering capabilities.
But the sources suggested that intelligence successes, both in preventing embassy attacks and aiding in the arrest of more than 40 suspected terrorists since 1993, may have contributed to the decision by whoever was behind the bombings in East Africa to pick the embassies in Nairobi and Dar es Salaam, both of which were deemed low security risks by the State Department.
The prevention of the two more advanced plans aimed at US embassies was first disclosed to Congress by the CIA Director, Mr George Tenet, last year. He gave no further details and did not mention the three other more nascent plots unravelled by his agency.
The plots, the sources said, did not involve embassies in Africa.
"I think it is fair to say that if you go beyond the target of embassies to American facilities and personnel, it is a very long list of bad things that have been prevented from happening by good intelligence that was properly acted on," said Mr Porter Goss (Republican, Florida), chairman of the House Select Committee on Intelligence and a former CIA case officer.
Mr Robert Oakley, former State Department co-ordinator for counter-terrorism, said on Monday that elaborate means are sometimes used to infiltrate terrorist groups targeting US facilities. He recalled an episode in the 1980s when US intelligence recruited a terrorist who had been assigned to bomb a US embassy in Europe. The putative bomber was allowed to detonate a bomb inside the embassy compound in such a way that little damage was done so that his relationship with US intelligence wasn't exposed, he said.
Since the bombings, State Department officials and members of Congress have called for substantial funding increases to bring most or all US embassies up to security standards recommended in the mid-1980s by a panel on diplomatic security headed by retired Admiral Bobby Ray Inman.
But beyond the so-called Inman standards, which call for 75-foot setbacks from the street and nine-foot walls at all embassy compounds, Mr Goss emphasised the need to realign US intelligence capabilities, once arrayed primarily against the Soviet Union to combat global terrorism.
He also noted that the Clinton administration had cut back on the number of CIA stations operating in Africa. However, a senior intelligence official said that both Nairobi and Dar es Salaam were not among the capitals to lose an intelligence presence.
Intelligence sources with knowledge about the CIA's work last year circumventing planned attacks on embassies said every agency success breeds a change in tactics by terrorist groups, which often spend as much time studying the CIA as the agency spends studying them.
The result, the sources said, has been tighter compartmentalisation of terrorist operations, where cells responsible for planning an attack have no knowledge of who assembles the explosives and those building the bombs do not know who will detonate them.