Kim Hak-hee and Lee Soo-ok were seized at an airport in Kuala Lumpur on Tuesday, while waiting for a flight to Beijing from where they allegedly planned to go to North Korea.

They were immediately extradited by the Malaysian authorities.

The arrest warrants were issued under South Korea's strict national security law, which prohibits its citizens from visiting the North without government permission.

Technically, the two Koreas remain at war after the 1950-53 Korean War ended without a peace treaty.

The BBC correspondent in Seoul, Andrew Wood, says that defections do happen, but usually from the communist, famine-stricken North to the more developed South.

About 200 North Koreans have escaped to South Korea in the past three years.

On the run since 1993

It was apparently not their devotion for communist ideology that led the pair to leave South Korea for the North.

The authorities have been seeking them since they fled to Indonesia in 1993, after Mr Kim's business had gone bankrupt. According to the South Korean state news agency, Mr Kim is charged with defaulting on his trading company's debts.

He was quoted as telling police that he had decided to defect to North Korea because he was a wanted man and could not return home.

The pair are alleged to have made contact with North Korean diplomats in Singapore and made plans to defect to North Korea by travelling through China first.