Prime Minister Raila Odinga of Kenya blamed terrorists for an explosion that badly damaged a shopping centre in downtown Nairobi, injuring at least 33 people, at midday on Monday.
He described the blast as a heinous act and insisted Kenya would not be cowed.
Several eyewitnesses say the explosion occurred just after they saw a man leave a bag at the centre in Moi Avenue.
The initial cause of the blast was thought to be an electrical fault, but police say they no longer believe this to be the case.
Kenya Power has also ruled out any electrical malfunction as the cause of the blast.