An Egyptian terrorist group financed by a fugitive Saudi Arabian Islamic fundamentalist is now the leading suspect in the twin bombings that killed 257 people at the U.S. embassies in Kenya and Tanzania, according to U.S. law enforcement and intelligence officials.

According to U.S. officials who asked not to be identified, a Kenyan security guard at the U.S. Embassy in Nairobi picked an operative in Saudi multimillionaire Osama bin Laden's terrorist network out of a spread of photographs shown to him by FBI investigators in Nairobi. Law enforcement officials said the FBI included pictures of several known bin Laden associates in the photos that are being shown to eyewitnesses to the blasts in Nairobi and Dar es Salaam.Although the guard said he had seen the man near the Embassy in Kenya, law enforcement officials said they consider the identification tentative and cautioned that it is likely to be weeks or months before they can pin down responsibility for the blasts.

"It will take at least four more weeks to complete the examination of both bomb sites and witness interviews, and from that we will develop leads," said assistant FBI director Thomas Pickard, the head of the bureau's criminal investigations division.

Nevertheless, both intelligence and law enforcement officials in Washington, who also agreed to speak only on the condition of anonymity, said intelligence and other evidence increasingly suggests that the synchronized bombings may have been the work of Egyptian Islamic Jihad, a terrorist group supported by bin Laden, a wealthy member of a prominent Saudi family who now lives in Afghanistan.

The State Department Friday closed the U.S. Embassy in Tirana, the Albanian capital, for all but emergency business after receiving what one Department official called "very credible" warnings that the Egyptian group is planning an attack on the post.

The attacks in Africa "have the fingerprints of Egyptian Islamic Jihad," said Vincent Cannistraro, a former head of counter-terrorism operations at the CIA. Officials in the CIA's Operations Directorate and Counter-Terrorism Center agree, and have circulated memos naming the Egyptian group, also known as al-Jihad, as the most likely culprit in the bombings. In July, the group warned that it was preparing to attack American targets.

According to U.S. intelligence officials who agreed to speak only on the condition of anonymity, an exhaustive review of electronic intercepts of the traffic on bin Laden's communications network has uncovered some evidence that bin Laden helped plan the attacks, along with some congratulatory messages after the Aug. 7 bombings in Nairobi and Dar es Salaam.

The officials also said the leader of al-Jihad, Aman al-Zawahiri, and Ahmed Rifai Taha, the leader of the Gama'a al-Islamiya, another radical Egyptian group, have joined bin Laden at the fugitive Saudi's base in Afghanistan. In addition, the officials said, U.S. reconnaissance satellites photographed bin Laden's Afghan camps being moved immediately after the attacks.

The bombs used in the African attacks, Cannistraro said, were similar to some used in the past by the Egyptian al-Jihad group. Evidence collected in Nairobi and Dar es Salaam, he said, indicates the bombs used there were made of ammonium nitrate and fuel oil and probably detonated by a high explosive primer, perhaps Semtex, the Czech-made plastic explosive widely used by a number of terrorist groups.

Although crude, such devices can be powerful. A similar fertilizer-and-fuel oil bomb destroyed the Federal Building in Oklahoma City, and a mix of 50 pounds of fertilizer and a modest amount of motor oil is enough to destroy a large truck.

The size of the bomb crater outside the U.S. Embassy in Tanzania, along with other evidence, indicates that bomb there could have been enhanced by using a cylinder of compressed propane or another gas to help concentrate the force of the explosion. Egyptian Islamic Jihad, Cannistraro said, has used such gas-enhanced devices to attack members of Egyptian Pres. Hosni Mubarak's government.

CIA analysts also have concluded that several communiques claiming responsibility for the attacks on behalf of something called "The Islamic Army for the Liberation of the Holy Shrines" used language almost identical to that in a "fatwa," or religious decree, in which bin Laden urged his followers to "kill American everywhere."