North Korea is apparently trying to assassinate South Korea''s defense chief Kim Kwan-jin known for his hard-line stance against Pyongyang, government sources here said Wednesday. "The defense minister is a key official and we''re always keeping close tabs on his security," one source said. "When he has to leave the office for functions and other commitments, we do take extra care." Another source said the military and intelligence officials are trying to determine the number of would-be assassins, and whether they are North Korean agents sent by Pyongyang or foreign nationals who entered the South from a third country under a North Korean order, according to South Korean (Yonhap) News Agency. The source said the assassins could also be North Korean agents already stationed in the South. Kim has been reportedly escorted by armed military police officers in plain clothes when venturing outside his office. Since assuming the post last December, Kim has taken tough stance on North Korea for its deadly provocations in 2010 that killed 50 South Koreans. The former Army general has called on South Korean forces to respond immediately to future North Korean provocations. North Korea has frequently balked at Kim''s remarks and its state media has dubbed him an "anti-North Korea confrontation maniac" and a "traitor."