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North Korea is carrying out extensive cell phone surveillance to identify and imprison citizens attempting to communicate with the outside world, a new report claims.

Sophisticated mobile surveillance technology capable of recording full conversations, location tracking, and signal jamming is being deployed, according to 17 North Korean defectors interviewed by Amnesty International.

The punishments for using phones to contact people outside North Korean borders ranges from a year's imprisonment at a reform facility to a lengthy term at a political prison camp, defectors cited in the 58-page report, in a crackdown that has heightened since Kim Jong-un came to power in 2011.

The nature of the technology is not identified in the report, but an independent expert told VICE News that the backpack-sized devices described by some defectors had the hallmarks of IMSI catchers — also known as Stingrays — which are portable phone surveillance devices that can intercept calls, text messages, and data, among other functions.

"The description sounds exactly like the modern IMSI catcher, which would be in a backpack and have a PDA or cellphone to control the device," said Richard Tynan, a surveillance technology expert who works for global surveillance watchdog Privacy International.

"Passive IMSI catchers may be able to do the cross border interception depending on whether they can break the 3G. Some of the other devices could be things along the lines of audio recording systems from far away.

"Location tracking for mobile phones is a very high priority for some governments," he added.

The report is likely to raise questions over whether Western-made surveillance technology is being used by North Korea. Some of the interviewees in the Amnesty report said that they suspected the technology had been made by Western countries, although this could not be verified by the authors.

"In theory there are sanctions in place in many countries in the world where the direct export would ordinarily be denied or prohibited," said Tynan. "But there does tend to be tech showing up in many countries that have embargoes against them."

The North Korean state owns all telecommunications, postal, and broadcasting services, and there is no independent media. However, phones smuggled from China are routinely used to circumvent state surveillance, the report stated.

The so-called "Chinese cell phones" allow North Koreans close to the Chinese border to avoid connecting to North Korea's Koryolink domestic network by connecting to Chinese cell phone networks. This puts them out of the reach of any network surveillance carried out by Koryolink, but IMSI catchers — portable devices which intercept communications by masquerading as a mobile phone mast — would enable the North Korean authorities to identify individuals connecting to Chinese networks.

Speaking to individuals on the phone outside of North Korea is not illegal, but the trade in Chinese cell phones is. Individuals caught may be charged with brokerage or illegal trade or, if speaking to people in South Korea or another country labeled as an enemy, a more serious charge of treason.

Three of the individuals interviewed by Amnesty had offered to pay the authorities when caught making a call outside the country or watching foreign media, and two out of the three were released after paying the bribe.

North Korea has increased efforts to clamp down on the use of Chinese cell phones since the ascendance of Kim in 2011, according to a spokesperson for another international NGO that works with defectors.

"It does seem like they've increased efforts," Sokeel Park, director of research and strategy for Liberty In North Korea, told VICE News. "And it's not just on the phone calls but the spread of digital media including TVs and micro SDs and so on. All of these things are points of information contamination."

"Thousands [of phone calls] are happening every day from South Korea to North Korea and it's not as well known in the outside word because it's usually just North Korean refugees quietly making contact — or trying to get money back in."

The crackdown was unlikely to deter North Koreans in the long run, he claimed.

"You can mobilize more policing and increase the punishments, try and root out corruption and all these things, but there's such a strong demand that all you're really doing is forcing people to be creative, increasing bribe costs, and maybe slowing it down."

Arnold Fang, East Asia researcher at Amnesty International, said the North Korean authorities were targeting people using cell phones "to maintain their absolute and systematic control."

"Kim Jong-un is being deceitful when he justifies such repression as necessary to stop what he calls 'the virus of capitalism.' Nothing can ever justify people being thrown in detention for trying to fulfil a basic human need — to connect with their family and friends," he said.

"The absolute control of communications is a key weapon in the authorities' efforts to conceal details about the dire human rights situation in the country."

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