Tightly controlled Turkmenistan has banned broadcasters from showing sex and encouraging "bad habits" in a law designed to create a "positive image" of the Central Asian country on the air.

The law, signed by strongman President Gubanguly Berdymukhamedov over the weekend according to state newspaper Neutral Turkmenistan, cites "protection of minors" as the reason for the ban on erotic content.

While the legislation does not specify what "bad habits" broadcasters should avoid promoting, Berdymukhamedov's government has waged a war on smoking in the republic of five million.

The document equally does not explain how content will be judged "pornographic" or "sexual-erotic".

In practice, television channels have long shown versions of foreign films with sexual and suggestive scenes edited out.

The new law also says broadcasters must aim "to create TV and radio programmes (showing) a positive image of Turkmenistan."

Press freedom watchdog Reporters Without Borders says Turkmenistan suffers from an "ever-growing information 'Black Hole'" and placed it 178th out of 180 countries in press freedom index.