Charlie Sheen under investigation by Los Angeles police

Officer Matthew Ludwig told AFP the probe was launched on March 31 in connection with a case in which Sheen was listed as a suspect.

"The Los Angeles Police Department threat management unit are the lead investigators on this case and the victim's information is confidential," Ludwig said, adding that a search warrant had been obtained in the case.

He did not elaborate on the nature of the probe or what prompted it, but several media reports said it was linked to claims that Sheen had threatened to kill his ex-fiancee Scottine Ross.

Variety magazine said that in an "alleged audiotape," Sheen was apparently heard threatening to hire a hitman for $20,000 to kill Ross.

Sheen also allegedly admits in the tape to having lied to a sex partner about him being infected with HIV, Variety said.

READ: Charlie Sheen says paid millions to blackmailers to keep HIV secret

Sheen and his publicist could not be immediately reached for comment.

The "Two and a Half Men" star was engaged to Ross in 2014 but they never married.

He revealed in an interview in November that he is HIV-positive and that his bad boy days were over.