NAIROBI, Kenya (AP) — Three people, including two police officers, were killed Wednesday morning in an attack by al-Shabab extremists in northern Kenya, Kenyan police have announced.

The victims were in a police vehicle when they were attacked between the Hayley Lapsset Camp and Garissa town, northeastern Kenya police chief George Seda said in a statement.

The attack began when the police vehicle was demobilized when it hit an explosive device planted on the road, said police and witnesses.

The attackers then fired a rocket-propelled grenade which killed two officers and a civilian, said the statement. Several other people escaped into the bush and their whereabouts are still unknown, it said.

The attackers then set the vehicle ablaze. The area is near Kenya's border with Somalia.

Police are pursuing the attackers and more officers have been deployed to the area to search for those missing from the vehicle, said the statement.

Al-Shabab, Somalia's homegrown extremist rebel group that is allied with al-Qaida, is suspected of carrying out the attack by has not yet claimed responsibility. Police say intelligence reports show there are pockets of extremists who have come from Somalia on a mission to carry out violent attacks in Kenya.

On Saturday night, police fought off an attempt by suspected extremists to seize control of a police station in Kutulo, Mandera County.

A group of rebels had targeted the Elram Anti-Stock Theft Unit using rocket-propelled grenades and rifles but the officers on duty fought back and repelled the attackers, said the police statement. No injuries were reported in the attack but the station's communications tower was slightly damaged, said the report.

The attackers escaped toward the nearby Kenya-Somalia border, said police.

Kenya's security agencies are on alert following the two attacks and reports that al-Shabab rebels are planning more attacks, said the statement.