In a major encounter with the Maoists in Jharkhand, 13 policemen have been killed when the ultras triggered a powerful landmine blast.The blast occurred at Salo jungle near Bargarh Panchayat under Bhandaria police station in Garhwa district this morning.District Information Officer of Garhwa A. Kumar told AIR Ranchi correspondent that the encounter is still on between the Maoists and the police.More forces have been rushed to the spot. He said the officer in Charge of Bhandaria police station is missing.