The United States has offered a $2 million (£1.2 million) reward for information leading to capture of the bombers of its embassies in Nairobi and Dar es Salaam.
The reward was announced as it was revealed in the Tanzanian capital that a number of people - Iraqis and Sudanese - had been arrested.
Police Commissioner Wilson Mwansasu said: "We have made some arrests." But he could not say how many or whether those being held were considered prime suspects.
The US Secretary of State, Ms Madeleine Albright, announced the reward yesterday and said the terrorist attack "tested our faith" but that the US's diplomats were prepared to fight for "justice and freedom" around the world.
"These United States, this principled, purposeful nation, will not be intimated," Ms Albright said, her voice rising with emotion.
"We will meet our responsibilities and stay engaged in the world. . . [and] keep standing up for the values that the peacemakers cherish and the future that the bomb throwers fear."
In Nairobi, rescuers have all but given up hope of finding any more survivors under the Nairobi rubble. The Kenyan president, Mr Daniel arap Moi, said yesterday there are probably no more survivors in the rubble of the building which collapsed on Friday.
"I don't think there are any human beings alive inside now", he said, when he visited the site before it was evacuated due to the risk of more buildings in the vicinity collapsing.
Meanwhile, Israeli rescuers had said a Kenyan woman, buried in the crumpled office block, could still be alive.
Known only as Rose, she has been pinned under hundreds of tonnes of masonry felled by the explosion beside the American embassy. The rescuers said yesterday morning that they could hear tapping coming from the huge mound of rubble but later lost communication with her.
At least 200 people were killed in the Kenyan capital and nearly 5,000 injured. At least 10 were killed and more than 70 injured in a nearly simultaneous blast at the American embassy in the Tanzanian capital, Dar es Salaam.
A Tanzanian police chief said yesterday that "some suspects" had been arrested in connection with the bombing. Commissioner Wilson Mwansasu said, however, that he had no idea how many people were held or if they were considered principal suspects.
In Washington, the US Assistant Secretary of State for African Affairs, Ms Susan Rice, said she had heard from Tanzanian authorities that three groups of suspects had been arrested.
The bodies of 11 dead American embassy staff were yesterday flown out of Kenya bound for the US. A growing body of testimony from survivors indicates the Nairobi attack was carried out by men who drove a vehicle into a car park behind the embassy before detonating a bomb.
The emerging picture has a pick-up truck entering the parking lot, driving past a first car park attendant before getting stopped at a second check as it tried to enter a car parking space beneath the embassy. Several survivors, including a number of embassy staff, report hearing an initial grenade-type explosion preceding the massive explosion. There are also reports of a gunfight prior to the big blast.
"It sounds like there was gunfire", an American embassy spokesman said yesterday. "I spoke to a woman working nearby who heard the rat-tat-tat of gunfire. But unfortunately most of the eyewitnesses died in the explosion."
It has been suggested that an embassy camera monitor was alerted to what was happening outside the premises by short-circuit cameras affixed to the wall. However, embassy officials have not as yet revealed any information about video recordings.
Both American and Kenyan police investigators are interviewing survivors who might be able to help build up a reliable sequence of events in the minutes leading up to the explosion. "We've got reports of shooting and of two people running away from the scene before the bomb went off," a Kenyan police spokesman told The Irish Times. "We're still trying to establish if it was a suicide bomb or if it was set off by remote control." Israel army radio reported yesterday that the device probably contained powerful Semtex plastic explosive. The use of such material would point to the involvement of a sophisticated terrorist group with a most lethal armoury. However, no firm links have been established with any of the groups, mainly Islamist fundamentalists, who have been blamed for, or claimed responsibility for, the attacks.