A group of 13 North Korean defectors who worked at a restaurant in China have recently begun to resettle in South Korea after undergoing Seoul's probe into what caused their massive defection in April, Seoul's unification ministry said Tuesday.

In early April, one male manager and 12 female workers who worked at a Pyongyang-run restaurant in the Chinese eastern port city of Ningbo defected to South Korea en masse.

The Ministry of Unification said that it is true that they have begun to resettle in South Korea, but it cannot reveal further details due to concerns over their safety.

The high-profile defection came as North Korea was slapped by the U.N. Security Council's tougher sanctions in March over its fourth nuclear test in January and long-range rocket launch the following month.

The rare massive defection has garnered attention over whether the sanctions have a major impact on pressuring North Korea, as Pyongyang-run restaurants in foreign countries have served as one of main sources of hard currency for the North.

But the case has also sparked a row in South Korea over whether they defected to Seoul of their own free will following North Korea's repeated claims that the female workers were abducted by Seoul's spy agency.

The National Intelligence Service has held them under its protection without sending them to a state-run resettlement facility, saying that the case is a high-profile defection and North Korea is using it as propaganda.

Usually, North Korean defectors receive three months of resettlement education at the facility named Hanawon after coming to South Korea.

An association of progressive lawyers requested a local court to decide on the legality of Seoul's protection of the defectors in a bid to clarify North Korea's claim that they were kidnapped by Seoul.

Restaurants operated by North Korea in foreign countries have served as one of the main sources of hard currency for the country.

The North is suspected of using the money to bankroll its nuclear and missile programs.

North Koreans employed by foreign restaurants are among the

50,000 workers sent abroad by the regime to earn much-needed hard currency to help it tackle economic hardships amid the U.N. sanctions on the North.

In the wake of the April defections, three more North Korean restaurant employees working in China escaped to Seoul in June. (Yonhap)