"We believe there's a connection between the threats we're getting from al-Shabab and other al-Qaeda-affiliated groups and the attack in Nairobi," Ugandan police Inspector General Kale Kayihura told reporters Tuesday, although he did not offer any evidence or an explanation of why he thought there was such a link.
Kenyan police officials said they were not ruling out the possibility that terrorists were behind the attack but so far had not established a connection between al-Shabab and Monday's attack.
As of Tuesday night, no group had asserted responsibility for the explosion, but the immediate suspicion of al-Shabab underscores the degree to which the radical militia is perceived as a regional threat. The militia orchestrated twin suicide bombings in July in the Ugandan capital, Kampala, killing 79 people as they watched the World Cup.
Monday's attack, which unfolded at a central Nairobi bus station, took place hours before Kayihura had warned of the possibility of more attacks by al-Shabab during the holiday season. On Tuesday, he said that there was "a strong possibility that these groups might want to repeat their diabolical plans."
Additional foot and motor police units had been deployed to secure Uganda's borders with Kenya and Sudan, as well as to patrol Kampala, Kayihura said. In Nairobi, security was bolstered on the streets, and Kenyan President Mwai Kibaki vowed publicly to apprehend the assailants.
"The security of our people is paramount. No efforts will be spared to ensure that security is beefed up," he said in a statement.
Kenya's police commissioner, Mathew Iteere, told reporters Tuesday that the attacker had boarded a Kampala-bound bus carrying a Russian-made grenade in a plastic bag. But at the prospect of a security search, he dropped the bag, which exploded. Iteere described the man as aTanzanian citizen who had been radicalized. It was unclear, he added, whether there were accomplices.
"In these incidents which have happened, we have found that most people perpetrating this type of crime are people who have recently converted to Islamic faith," Iteere said. "These are the people who have been radicalized and indoctrinated."
Kenya and Uganda both support Somalia's government, which al-Shabab is trying to topple, and the militia has vowed in recent years to attack Kenya. Kenya has been the target of previous terrorist attacks, including the 1998 bombings of the U.S. embassies here and in Tanzania.
By Sudarsan Raghavan