A Kenyan official says a roadside bomb suspected to have been planted by extremist in the northern Kenyan town of Mandera, near the Somali border, wounded five policemen, three of them seriously.

The attack comes a day after one Kenyan soldier died and two others were wounded in an ambush in Mandera by al-Shabab Islamic extremists from Somalia.

The official, who insisted on anonymity because he was not authorized to speak to the media, said Monday the five policemen were on patrol near the Somali border when the bomb blew up their truck. He said three policemen are to be flown to Nairobi for treatment.

Kenya has experienced a wave of retaliatory attacks by al-Qiada-linked al-Shabab since it sent its troops to Somalia to fight the extremists in 2011.