Jordan's former Crown Prince Hamza bin Hussein said in a video recording on Saturday he was under house arrest.
The country's military had told him to halt actions used to target the country's "stability and security".
People familiar with the matter said this could be related to a plot to 'destabilise the country'.
Hamza said in the video, passed by his lawyer to the BBC, that he was not part of any foreign conspiracy and denounced the ruling system as corrupt.
In state media, the military warned Prince Hamza was part of a broader, ongoing security investigation in which a former minister, a junior member of the royal family and unnamed others were detained.
Earlier army chief Yusef Huneity denied reports that Hamza had been arrested.
The authorities have become increasingly concerned with his efforts to build ties with disgruntled figures within powerful tribes.
King Abdullah dismissed Prince Hamza as heir to the throne in 2004 in a move that consolidated his power.
Prince Hamza is not seen as a major threat to Jordan's monarchy and has been marginalised for years, but this move against him represents the first such incident involving a close member of the royal family since King Abdullah came to the throne.
Government officials were not immediately available for comment.