A North Korean man waits outside the border crossing between North Korea and Dandong, China's largest border city with North Korea, in Liaoning Province, on May 30. Pyongyang has been blocking wireless signals from China in an ongoing crackdown against defectors. File Photo by Stephen Shaver/UPI | License Photo

SEOUL, Sept. 22 (UPI) -- North Korea is blocking wireless signals along the China border, preventing mobile phones operating on Chinese memory chips from receiving calls.

A source located at the China-North Korea border, speaking to Yonhap on the condition of anonymity, said Pyongyang has stepped up its restrictions on cellphone reception along its 808-mile border with China. Signals from Chinese cellphone towers increasingly are unable to reach Chinese SIM card-equipped phones in North Korea, the source said.


The move follows recent trends in the reclusive country that are reversing a general movement toward greater mobility seen in the last years of Kim Jong Il's rule.

Since Kim Jong Un fully assumed power in 2012, North Korea has tightened control at the China border, and the state has heightened surveillance of mobile phones in addition to building walls to make defections more difficult.

The source said the North Korean leader mandated the blocking of signals in order to prevent communication between North Koreans seeking to escape and brokers on the other side of the Yalu and Tumen Rivers.

South Korean news network YTN reported the jamming of signals has been ongoing under Kim's rule, but with the rise of Workers' Party cadre defections, the North Korean leader has implemented stronger measures to restrict North Korean communication with the outside world.

The new mandate is expected to have an impact on areas where border crossings frequently take place, including the cities of Hoeryong and Musan in North Hamgyong province, Hyesan in Yanggang province and Manpo in Jagang province.

North Korea's jamming of signals is also affecting communication networks in neighboring China, and telecommunications representatives in China's Changbai region had crossed into North Korea to submit a request to cease the transmission block, but their request was rejected.

North Korea has also been using cellphone detectors at the border to confiscate China-made phones from being used in the country. The source said it is harder to cross into North Korea undetected because Pyongyang has deployed increasingly sophisticated technology to root out foreign phones.