North Korea has cracked down on the increasing use of cell phones, saying the devices provide a means for toppling the government, a report says. A document released to senior members of the Worker\'s Party of Korea listed a number of new restrictions on cell phone use in the reclusive communist country, the Japanese newspaper The Mainichi Shimbun reported Thursday. The regulations were required, the document said, because mobile phone users were \"spreading cultural ideology based on capitalism\" and \"threatening the safety of the country and the revolutionary leadership.\" The increased use of cell phones in North Korea had become \" a means for the United States to overthrow the government,\" the memorandum said. Officials were ordered to block \"polluted\" messages and prevent the use of mobile phones to spread information. Users must now register their personal information and mobile phone number when purchasing a cell phone. The ministry of information also ordered mobile phone companies not to connect to foreign networks near the border and disable cell phones that play music and display images. More than 2 million North Koreans have cell phones, twice the number 16 months ago.