A group of North Korean defectors who used to work at a restaurant in China entered South Korea last week via Thailand and Laos, a source familiar to North Korean affairs said Monday.

Thirteen North Korean workers at an overseas restaurant defected to South Korea en masse last week amid toughened international sanctions on Pyongyang over its latest nuclear and missile tests.

The source said that the North Koreans who worked at a restaurant in the Chinese eastern port city of Ningbo flew into Bangkok early last week and moved to Laos taking a land route. In Vientiane, they left for Seoul late Wednesday and arrived here the next day, it said.

The government has declined to comment on their defection route and other details, citing the issue's sensitivity and diplomatic aspects.

Seoul's unification ministry on Friday made an unusual announcement about their mass defections in a breakaway from its low-key stance on the issue of North Korean defectors.

North Korean restaurants have served as one of the main sources of dollars for North Korea, which is suspected of bankrolling the North's nuclear and missile programs.

Many restaurants run by North Korea have recently faced business hardships, with some shutting down following stronger international sanctions.

Seoul also has asked its nationals not to use North Korean restaurants in China and Southeast Asian nations in a bid to hit the source of income for Pyongyang.

North Koreans at overseas restaurants are among some 50,000 workers sent abroad by the regime to earn hard currency, a move aimed at averting a series of past U.N. sanctions.

South Korea estimates that North Korea is running approximately

130 restaurants in some 12 countries including China, Vietnam and Cambodia, earning $10 million annually.

Meanwhile, the government is under fire for its rare announcement of the North Koreans' defection as critics said that Seoul is seeking to influence the upcoming general elections slated for Wednesday in its favor.

The ruling party and the government often highlight North Korea-related news to raise awareness about security ahead of key elections, a move to rally conservative and security-concerned voters.

Seoul's unification ministry denied a local newspaper's report that Cheong Wa Dae ordered the government to make public the latest mass defection.

"(From now on), the government can unveil further cases of defections if they are unprecedented and meaningful," Jeong Joon-hee, a ministry spokesman, told a regular press briefing.

He declined to confirm whether there are more North Koreans at the same restaurant on a waiting list for defection. (Yonhap)