South Korea says its intelligence service has intercepted two North Korean spies.  The two apparently arrived in the South with an assignment to kill a prominent defector from the North.

South Korean authorities say they have detained two North Korean military officers who entered the country earlier this year disguised as defectors.

Roughly 2,000 North Korean defectors enter South Korea year.  Like many of them, the two 36-year-old detainees passed through Thailand before flying to the South.  All defectors undergo questioning by South Korea's intelligence service, which reportedly uncovered the two as spies.

News reports say both men confessed to acting on orders to plan the assassination of 87-year-old defector Hwang Jang-yeop, who entered South Korea in 1997.  Hwang was once a senior official in the Pyongyang government and a teacher of its present leader, Kim Jong Il.  He is now one of Pyongyang's harshest public critics, and moves under extremely tight security.

Lee Sang-hyun specializes in inter-Korean security issues at the Sejong Institute in Seoul.

Lee says after Hwang arrived the South Korean government was trying to engage the North, and wanted to keep his profile low.  Now, however, the more conservative administration of President Lee Myung-bak has made it easier for Hwang to visit the United States and Japan, and he is better able to embarrass the North.  So, Lee thinks North Korea felt it was time for a more stern response.

The spy investigation comes at a sensitive time, as many South Koreans think Pyongyang had a role in the sinking of a South Korean naval vessel last month.

A total of 46 sailors died in the sinking, which was near a maritime border Pyongyang disputes.  Investigators concluded an "external explosion" sank the ship, but they have not yet what caused the blast, and have not confirmed any North Korean involvement.

Chung Mong-joon, the head of South Korea's ruling Grand National Party, describes the capture as a drama fit for a movie.  But, he adds, it is not new for North Korea.

He says there have been numerous acts of espionage staged by North Korea, but it continues to deny its involvement in any of them. This reminds South Koreans, he says, that even though reuniting with the North is our task, the North continues to pose a present danger.

Despite substantial evidence, North Korea has never admitted a role in the 1987 mid-air bombing of a Korean Air jet that killed all 115 people aboard.  Pyongyang also denies it orchestrated a 1983 bombing in Burma that killed three South Korean cabinet officials.