At least four Indian security forces personnel were killed and 36 others injured in an Improvised Explosive Device blast in the northeastern state of Assam Friday morning, a senior police official said. "The blast took place at Solmara in the state's Goalpara district when the Central Reserve Police Force troops were patrolling the area at 8 a.m.. The four were killed on the spot while those injured have been admitted to a local hospital where the condition of some are said to be serious," the official said. Preliminary probe has revealed that the National Democratic Front of Bodoland is behind the blast, he said, adding that a massive manhunt has been launched to track down those responsible for the blast. The National Democratic Front of Bodoland is a terror outfit which seeks to obtain a sovereign Bodoland for the Bodo people in Assam.