A clip from a sex tape said to feature Malaysian opposition leader Anwar Ibrahim has been posted on video-sharing website YouTube, reports said on Tuesday.

The one minute and 47 second excerpt uploaded on Sunday is not explicit in itself but is part of a longer video showing a man having sex with a woman in a hotel room, local media have reported.

The man in the YouTube clip is said to closely resemble Anwar, although the former deputy premier has denied any involvement.

YouTube removed the clip late Monday but by then it had spread to pro-government blogs and websites, according to the Star daily newspaper.

The Star said the YouTube clip showed a man in a towel with another man dressed in a shirt and trousers while a woman with Chinese features is seen sitting on a bed.

In the longer video, the man in the towel reportedly has sex with the woman after the other man leaves the room.

"The face of the towel-clad, pudgy-looking man in short hair can be seen several times. He, however, does not stand in place long enough for his face to be clearly identified," the Star reported.

Anwar told online news portal Malaysiakini that he was not the man in the video.

"Now, the video has been distributed. And whether the person looks like me or not, I don't care. It wasn't me," he was quoted as saying by the website.

Anwar's wife Wan Azizah Wan Ismail, accompanied by the couple's children, told reporters Tuesday that the family had viewed the video clip and that it was not Anwar on the tape.

"We as a family decided to watch the video posted on the Internet, and it is clear that the body and physique of the actor in the video is extremely different from the body and physique of Anwar Ibrahim," she said.

"(Whether the video is) authentic or not, that is not the issue. The point is that it is not Anwar in the video," she added.

Three men have claimed they obtained the tape, but two of them said they handed it over to police and were not responsible for the clip posted on YouTube, according to Malaysiakini.

Home minister Hishammuddin Hussein told state media the police were not involved in the release of the clip.

"Even I don't know where this clip on YouTube came from and police chief Ismail Omar has told me that the clip did not come from the police," he told the Bernama news agency. Ismail said later that police would carry out a "thorough investigation" into how the clip came to be on YouTube.

Last week, the police chief said experts had decided the tape was not doctored and a police investigation into it was in its closing stages.

The three have claimed that the incident took place at a hotel "that offered sex services and spa facilities" in the Malaysian capital on February 21 but a subtitle in Thai on the clip gives a Bangkok address.

Anwar, who was sacked as deputy premier and jailed in 1998 on sodomy and corruption charges widely seen as politically motivated, said the tape was another "dirty and obscene" attempt to end his career.

The latest allegations emerged as Anwar undergoes a second trial for sodomy, after a 25-year-old male former aide accused the 63-year-old father-of-six of sodomising him at an upmarket Kuala Lumpur condominium in 2008.