Kuwait has imposed a news blackout on an investigation into reports of a recording that implicates unnamed people in an alleged plot to overthrow the state's ruling system, state news agency Kuna said.

Kuwait's public prosecutor opened a case in December after a legal complaint which demanded an investigation into tweets about the alleged recording.

The topic has featured extensively in local media and prompted a rare statement from the ruler's office this week, which told people to stop discussing the case in order to preserve national unity.

The attorney general ordered that the investigation be made secret and banned publishing any information on "the existence of a tape that contains information and statements implicating some people of conspiring to overthrow the ruling system in the country and challenge the rights and authority of his highness the emir," according to the statement carried by Kuna.

The statement said all forms of communication were banned from discussing the case, including news outlets and social media. Such rumours were damaging to the country's interests, it said.

It said the prosecutor would inform media about the results of the case once the investigation was over. It came one day after the statement from the emir's office.

The Emir, Sheikh Sabah al-Ahmad al-Sabah, came to power in 2006 after his ailing predecessor stepped down. Sheikh Sabah's brother, Crown Prince Sheikh Nawaf Al-Ahmad Al-Sabah, is next in line to become emir in the 250-year-old dynasty.  - Reuters