North Korea could stage a terror attack in downtown areas in South Korea, Seoul's defense chief said Thursday, as South Korea keeps its troops vigilant against possible North Korean provocations.

   Defense Minister Kim Kwan-jin told lawmakers that the North could plot a possible terrorist attack by taking advantage of lax defense preparedness in South Korea's downtown areas.

   No terrorist attacks have occurred in Seoul since 1968 when 31 North Korean commandos infiltrated Seoul in a failed assassination attempt on then President Park Chung-hee.

   Kim also said the military holds regular training exercises in four areas that are home to nuclear power plants.

   Kim made the assessment to lawmakers, though he did not give any further details.

   The warning comes a week after a bipartisan group of U.S.

congressmen submitted legislation to re-designate North Korea as a state sponsor of terrorism for a series of provocations.

   North Korea torpedoed a South Korean warship and shelled a South Korean border island last year, killing 50 people, mostly soldiers, and plunging inter-Korean relations to their lowest level since the 1950-53 Korean War.

   The Obama administration said Tuesday it has not yet found enough evidence to relist North Korea as a state sponsor of terrorism.

   North Korea has a track record of terrorist attacks against South Korea, including the 1987 bombing of a South Korean airliner near Myanmar that killed all 115 passengers aboard.

   The attack prompted Washington to put Pyongyang on its terrorism blacklist, but the United States removed the North from the list in 2008 to facilitate the talks on ending the North's nuclear weapons programs. (Yonhap News)

This 2007 file photo shows that soldiers inspect an unidentified explosive discovered at a construction site in Seoul. (The Korea Herald)