North Korea is ramping up security at its borders and cracking down on cell phone use amid rising concerns over defections to the South, the Korea Times reported Tuesday. The government has reportedly doubled barbed wire on fences, set up surveillance cameras and planted mines along parts of the Tumen River, which separates North Korea from China.

The revelations are part of the White Papers on Human Rights in North Korea, a report published annually by the Korea Institute for National Unification, a South Korean state-affiliated organization. It also alleges that laborers are forced to work long hours in foreign countries. Most of their wages are withheld from them. The report cites individuals who have escaped North Korea since 2014 and now live in the South.

Much of the increased border security has been around Hoeryong and Muson, which sit alongside the Tumen River, as well as Onsong and Hyesan.

In recent years, North Korean leader Kim Jong Un has overseen a major crackdown on defections from the country. Last year, there were reports the reclusive state was boosting its border security after Kim ordered fences to be installed in areas where defections were believed to have taken place. News of defections has regularly prompted massive investigations. There are estimated to have been some 28,000 defections since the 1990s.

Defection is a criminal act in the state, which is considered among the world’s most autocratic. The Kim family dynasty has been accused of rampant human rights violations, including maintaining secret labor camps for government opponents where torture and starvation are routine. Religion and free speech are practically nonexistent in the kingdom, according to human rights groups.

The White Papers on Human Rights in North Korea are expected to be released in English in June. The report comes as North Korea faces growing international criticism for its recent military endeavors, particularly its claim to have tested a hydrogen bomb.