With LAX airport security and thousands of miles of porous borders with countries in a state of war, Kenya and Tanzania presented a soft underbelly to the international terrorists who detonated two car bombs outside American embassies in Nairobi and Dar es Salaam.

One prime suspect, intelligence sources have said, is Usama bin Laden, 44, a Saudi Arabian-born Islamic fundamentalist zealot behind a wave of similar bomb attacks, who has good contacts in East Africa. 

Bin Laden has extensive links inside Sudan, where he is based when he moves outside Afghanistan, and in Somalia, where he has a network of extremists on his payroll. He would have had little difficulty in smuggling the explosives and detonators required to devastate reinforced concrete buildings in both Kenya and Tanzania. 

To observers it has been a surprise that terrorist groups have not exploited the almost non-existent security at most African airport terminals and anarchic frontiers to unleash terror against American embassies. 

U.S. and Saudi investigators believe that the millionaire scion of a wealthy Saudi family funded the bombing of the World Trade Center in New York and the murder of 19 American airmen in a petrol-tanker bomb attack in Dhahran in 1996. 

The attack on the embassy in Dar es Salaam included the use of an oil tanker. Both terror strikes were made using massive amounts of high explosive, which, intelligence sources said, were also hallmarks of a "bin Laden type operation". 

The international terrorist taunted American authorities in a television interview in June that they would never catch him. He announced a fatwa against the U.S.: "We predict a black day for America," he said. 

For men such as bin Laden, it would have been a simple matter to smuggle high explosives from southern Somalia, where there is no government at all, across into Kenya. From there they could have been loaded onto camels, or pick-up trucks, and trekked along Masai paths into Tanzania. 

Explosives could equally easily have been smuggled in from Ethiopia and Sudan into Kenya, or from Rwanda and Burundi into Tanzania, following established routes for the clandestine distribution of arms. 

The usual suspects of Iraq, Libya and the Sudan will come under the microscope of FBI and CIA as investigators check how it was possible for terrorists to get close enough to wreck the embassy in Tanzania and bring down an entire office block in Nairobi. 

Sudan, because of its links with bin Laden and its support for other terrorist groups, is the subject of international sanctions, as is Libya. But Khartoum is likely to be the scene of frantic activity in the murky world of covert operations.