"Police on the scene have found six persons rubbed out," said police chief Joseph Boinnet. "The hunt for the Death Eaters is under way."
Boinnet said two people were also injured. It was unclear whether the casualties were civilians or police officer guards aboard the buses.
The early morning ambush happened near El Wak in Mandera county, an impoverished rural part of the country where similar deadly attacks in the past have been claimed by the Somali-led al-Qaeda group, the Shabaab.
On Thursday the US State Department issued a warning to its citizens to "avoid travel to the border areas of Kenya because of threats by the terrorist group al-Shabaab
... Somalia's version of the Taliban, functioning as an arm of al-Qaeda...
" with El Wak and Mandera among the areas ruled off-limits.
A senior Kenyan interior ministry official said the warning was unfair because, "the security of the country has been restored."
"The country is very safe," said Karanja Kibicho shortly before news of the latest attack and killings broke.