( CNN ) -- A bus explosion that killed one and injured dozens in Kenya was caused by a man believed to have ties to a militant group , authorities said Wednesday . The grenade attack Monday injured at least 40 people in a Uganda-bound bus , Kenyan police spokesman Eric Kiraithe said . It left blood stains and luggage scattered at the site of the attack in Nairobi 's central business district . Most of the injured were Ugandans headed home for the holidays , the spokesman said . He said the suspect , a 35-year-old Tanzanian , was the only fatality in the attack . It was unclear whether he had accomplices . `` Police suspected him because he was quite nervous and resisted attempts to have his luggage examined , '' Kiraithe said . After an altercation with the police , the suspect dropped his bag , which exploded . `` We have strong reasons to believe there 's a link between him and Al-Shabaab , '' Kiraithe said . He declined to comment on any evidence linking the suspect to the militant group that has been battling Somalia 's transitional government for years . The group , considered the al Qaeda proxy in Somalia , has previously threatened attacks on Uganda and Burundi . The two countries contribute troops to the peacekeeping effort in Somalia . Kiraithe said it is `` logical to believe he targeted the bus because it would have Ugandans . '' The bus was bound for Uganda 's capital , Kampala . The nation 's authorities had warned of holiday terror attacks by the Islamist group hours before the blast . Kenya and Uganda have boosted security along their borders . `` We are investigating the crime together with Ugandan authorities , '' the spokesman said . `` This is a busy travel period so we 're also adding more security and taking all measures to make sure it 's safe . '' Al-Shabaab has claimed responsibility for July twin bombings in the Ugandan capital that killed more than 70 people watching the World Cup .
One person killed , 40 more are injured in the bus blast . The suspect is a 35-year-old Tanzanian man , authorities say . Police spokesman says there are `` strong reasons '' to believe he 's tied to Somali insurgent group .