Five people, four of them police officers, were killed when their armoured police car ran over an IED in Baure area, Lamu, on Wednesday morning.
It is believed the device was planted by al Shabaab militants.
The officers were of the Mangai Rapid Border Patrol Unit in Lamu East while the fifth victim was a civilian.
Seven officers from the unit were on their way to Motown town in Lamu West to refuel the vehicle when the incident occurred at about 9 am.
They repulsed them and reported to the scene where they found the five bodies. The other two officers may have been abducted by the militants as they could not be found.
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Operation Linda Boni director James Seriani and county commissioner Joseph Kanyiri did not answer calls for comment on the attack.