A Kenyan official says five police officers have been killed by suspected Islamic extremists in the northern county of Mandera.

Mandera County Police Commander Job Boronjo said the officers were escorting a passenger bus early Monday when they were ambushed.

Boronjo said the bus driver sped away but the police vehicle came under attack. He said the police vehicle was set on fire and two of the victims were burned beyond recognition. Four officers survived.

Boronjo said the attackers are believed to have fled toward the Somalia border.

Kenya has been attacked several times by members of the Somalia-based Islamic extremist group al-Shabab, which opposes Kenya's military involvement in the East African country.