North Korea is believed to have closed more than 30 restaurants in foreign countries due to toughened international sanctions, a source familiar with the matter said Tuesday.

The North's move indicates that the regime faces difficulties in earning dollars as the U.N. Security Council's sanctions on Pyongyang are aimed at curbing the source of hard currency suspected of bankrolling the North's nuclear and missile programs.

The source said that since the imposition of the sanctions in March, the North is presumed to have closed or suspended over 30 restaurants in foreign countries.

South Korea estimates that North Korea is running approximately 130 restaurants in some 12 countries, including China, Vietnam and Cambodia, earning US$10 million annually, according to the government.

The North's restaurants abroad have been getting attention since April, when a group of 13 North Koreans working at a Pyongyang-run restaurant in China defected to South Korea en masse.

North Koreans in restaurants abroad are among some 50,000 workers sent out of the country by the regime to earn much-needed dollars to help it avert economic hardship under the string of past U.N. sanctions.

Another source said that North Korea has strengthened its monitoring and control over its workers abroad following the high-profile defection of restaurant staffers.

It said that North Korea-run restaurants abroad are known to carry out illegal business activities in China in a bid to boost falling revenues.

"Some restaurants in China are believed to push North Korean female minors into serving customers despite the visas issued by Chinese authorities only allowing them to hold performances at restaurants," the source said.

It estimated that around 350 to 400 North Koreans are working at restaurants run by North Korea in China with performance visas.

Of them, there are about 50 North Korean minors. (Yonhap)