North Korea has disabled video camera and memory card functions in new mobile phones, a news report said Saturday, in what appears to be Pyongyang's latest move to tighten control over the flow of information within and across its borders.

The North also removed the Bluetooth function, a protocol that allows mobile phone users to exchange data over short distances, and blocked subscribers from using mobile phones beyond the city where they are registered, Washington-based Radio Free Asia reported, citing a Japanese journalist familiar with the issue.

"Mobile phones have played a big role in spreading information," said Ishimaru Jiro, the publisher of Rimjin-gang Magazine, which is written by undercover journalists inside the North, according to RFA. With the technological restrictions, however, the new mobile phones "have lost key functions for the spread and proliferation of information inside and outside North Korea," he said.

Pyongyang took the new measures last October when it issued a new first four digit number to new subscribers, RFA said, in an apparent move to differentiate more than 1 million subscribers with phones equipped with camera functions and memory cards.

North Koreans can purchase phones using the previous four digit number and equipped with camera functions and memory cards, but the North has raised their price to about $1,000, putting them out of reach for ordinary citizens, RFA said.

North Koreans earn an average of 3,000 to 5,000 won a month. The North Korean won is traded at around 3,500 won to $1 in North Korean markets, though the official rate is 100 won to one dollar, according to North Korean defectors in South Korea.

The North's move appears to be designed to wean North Koreans off phones with high-technology and eventually restrict any free flow of information and foreign news and materials, which the North sees as a potential threat to its stability.

Besides the sanctioned mobile phones, some residents near the border with China are believed to be using Chinese mobile phones to keep in touch with relatives and friends in South Korea and China, thus becoming a key source of North Korean news to the outside world. (Yonhap News)