Kenyan and Ugandan officials have linked the blast to Al Shabab, the Somali militia that took credit for a July suicide bombing that killed 79 at two restaurants in Kampala, Uganda.
Al Shabab, the Somali militant group with ideological links to Al Qaeda, says the threat to attack Kenya – posted on its website this week – is fake.
It has massed troops on the Somali border. Islamist militias have threatened retaliation if Kenya acts.
The ethnic crisis is taking center stage at a three-day African Union summit in neighboring Ethiopia.