“Officers have been injured, we have sent a team to investigate,” regional police chief Leo Nyongesa said.
“Four officers have been injured, the tanker passed over a landmine,” said a police official who was not authorised to speak to reporters.
It was not immediately clear whether the explosion had been triggered by a remote device, nor who was responsible for the blast.
Last month the hardline Shebab warned Kenya of revenge attacks for sending tanks and troops into Somalia in October.
Kenya has been hit by a series of grenade attacks and explosions, mostly in Nairobi and in northern towns and camps housing Somali refugees close to the border.
Earlier this month attackers launched a deadly grenade attack on a restaurant in the port city of Mombasa.