North Koreans caught using mobile phones to call families abroad risk being sent to political prison camps under an increasingly iron-fisted regime that is jamming devices and stepping up surveillance, according to a report from Amnesty International.

Government efforts to keep North Koreans from learning about the outside world and to obscure awareness of human rights violations in the country coincide with the rise of gray markets, where citizens procure everything from food and clothing to SIM cards and DVDs, Amnesty International said in a report titled "Connection Denied: Restrictions on Mobile Phones and Outside Information in North Korea."

Amnesty International said it undertook the research to document how North Korean authorities are responding to the wider availability of new mobile technologies under the Kim Jong Un regime. More than 3 million subscribe to North Korea's domestic mobile phone service.