0608 GMT April 23, 2019
The police vehicle was moving from Kula Police Post toward the Liboi border town, North Eastern Regional Coordinator Mohamud Saleh said. He said three other officers were unhurt.
The incident came a day after Kenya's police chief Joseph Boinnet announced al-Shabab extremists were stepping up attacks in the country.
Boinnet said the Somalia-based al-Shabab is under pressure from African Union troops supporting Somalia's weak government against the extremist group's insurgency.
Al-Shabab, which has ties to al-Qaida, claimed responsibility for Wednesday's attack in a report by its news agency and said it had killed at least five Kenyan police officers, according to the SITE Intelligence Group, which monitors extremist groups.
In the last two weeks, attacks by al-Shabab in Kenya's Garissa and Mandera counties have increased after a lull. Last week, an improvised bomb killed four people in a vehicle, including a minor.
Mandera County has been hardest hit in recent years by an al-Shabab campaign to avenge Kenyan troop presence in Somalia since 2011.
Kenya's troops are part of the AU force in Somalia. Kenya has managed to stop the frequency of al-Shabab attacks in its capital, Nairobi, and major towns, but human rights groups say the government uses methods such as extrajudicial killings that can fuel revenge attacks.