North Korea has summoned its consuls stationed in Shenyang in order to investigate recent mass defections of restaurant workers at the North's state-run restaurants in China, a U.S.-based media report showed Saturday.

In April, a group of 13 North Korean employees at a Pyongyang-run restaurant in the Chinese eastern port city of Ningbo defected to South Korea en masse. In June, three more North Korean restaurant employees working in China escaped to Seoul.

The diplomats called in to Pyongyang in early July were reported to be in charge of supervising those areas where the defections took place, said Radio Free Asia (RFA), citing anonymous sources. They have been going through a rigorous review of their loyalty to the regime, it added.

Overseas restaurants are an increasingly important source of dollars for the North at a time when international sanctions have cut off Pyongyang from the outside world aimed to dry up the money needed to pursue missile and nuclear development.

North Korean overseas workers are usually proven loyalists of the regime and are more affluent compared to ordinary citizens.

They are allowed to work abroad and send back hard currency for the country. (Yonhap)