Six people were killed on Friday when suspected Islamist gunmen fired on two buses in Kenya's far northeast close to the Somalia border, police said.
"Police on the scene have found six persons shot dead," said police chief Joseph Boinnet. "The hunt for the terrorists 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 Shebab.
The deadliest raid was in November 2014 when gunmen flagged down a commuter bus, separated passengers by religion and executed 28 non-Muslims.
A similar raid in December 2015 left two people dead, after Muslim passengers shielded their Christian fellows.
The Shebab has fought to overthrow the internationally-backed government in Mogadishu since 2007, but turned its sights on Kenya when the army was sent into Somalia in 2011 to fight the Islamic insurgents.
Since then the Shebab has carried out frequent attacks on civilians in different parts of Kenya, including a Nairobi mall, a northeastern university and coastal villages.
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-Shebab" 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.