A blast has killed at least six people on a crowded minibus passing through a suburb of Kenya's capital, Nairobi, that has a large Somali population.
A grenade was thrown into the vehicle in the Eastleigh area, police said, ripping the roof and sides off the bus.
A number of recent attacks in Nairobi and Mombasa have been blamed on Somalia's al-Shabab militant group.
Earlier this year, Kenya sent troops into Somalia to pursue militants.
Kenyan forces ousted the Islamist rebels from their last Somalia stronghold, Kismayo, last month.
After Sunday's blast, police fired into the air to disperse crowds of youths who targeted Somali residents in retaliation.
Kenya began its intervention in Somalia nearly a year ago after a spate of cross-border attacks blamed on al-Shabab.