The assailants detonated the explosives as the police passed late yesterday in two vehicles and then opened fire with high caliber weapons, Interior Minister Francisco de Vargas said.
Manuel Escurra, 48, the police chief of the town of Horqueta in the northern province of Concepcion, was shot to death in the incident.
The police were responding to a call for help from a rancher who said guerrillas had tried to kidnap him.
Escurra was the 32nd person killed in guerrilla-related violence since 2007, when the Paraguayan Peoples Army (EPP) became active in Concepcion and San Pedro, another poor northern province.