North Korea has officially declared that it is blocking Facebook, YouTube, Twitter and South Korean websites.

The Ministry of Posts and Telecommunications announcement was shared this week at the country's main mobile service provider, Koryolink, and other places hosting Internet users.

The new restrictions will make it tougher for visitors or the small community of foreign residents in North Korea to share real-time information about the country with the outside world, and will also restrict the ability of North Koreans with Internet access to view information about their country shared elsewhere.

The government announcement termed YouTube, Facebook, Twitter, Voice of America and South Korean media sites as particular examples of what it is blocking "for a certain period of time." It also said gambling and "sex and adult websites" have been blocked.

The announcement also says that anyone who tries to hack onto such sites, enter them in an "improper" way or dispense "anti-republic data" from them will be subject to punishment under North Korean law.

In 2013, North Korea decided to permit foreigners in the country to use 3G on their mobile phones, which generally entails buying a local SIM card to get onto the Koryolink mobile carrier network.