UN experts have demanded an immediate investigation into allegations that Saudi Arabia's crown prince was involved in a plot to hack the phone of Amazon boss and Washington Post owner Jeff Bezos.

The UN special rapporteurs, Agnes Callamard and David Kaye, issued a statement on Wednesday, saying that they had information pointing to the "possible involvement" of Crown Prince Mohammed bin Salman of Saudi Arabia in the alleged 2018 cyber-attack, which preceded alleged threats by the National Enquirer to publish intimate photographs of Bezos.

The rapporteurs' report alleged with "medium to high confidence" that the billionaire's iPhone X was hijacked by a MP4 video file. Bezos received a WhatsApp message on May 1, 2018, which contained the MP4 video, from an account belonging to the crown prince. 

The report said that within hours of receiving the video file there was "an anomalous and extreme change" in the device's behavior, with the level of outgoing data from the phone jumping nearly 300-fold.

The UN rapporteurs based their report on a 17-page forensic analysis, which, according to several media reports, was commissioned and paid for by Bezos to unveil the truth behind the phone hacking.

The rapporteurs said they believed the hack was carried out "in an effort to influence, if not silence, The Washington Post's reporting on Saudi Arabia" and called for an "immediate investigation by U.S. and other relevant authorities."

It is reported an FBI investigation into the hack was ongoing, but so far the FBI declined to comment. However, Saudi officials dismissed the allegations as absurd.

The alleged hack deepens the intrigue around how the Enquirer - which had close links with U.S. President Donald Trump at the time of the alleged extortion - obtained messages exchanged between Bezos and Lauren Sanchez, an ex-TV anchor, who the tabloid said he was dating.

Last year Bezos' security chief said the Saudi government was the source of the messages. A month before, Bezos had accused the Enquirer's owner of trying to blackmail him with the threat of publishing "intimate photos" he allegedly sent to Sanchez.

"So sorry to hear the news about Jeff Bozo being taken down by a competitor," U.S. President Donald Trump gloated on Twitter as news of the clash between Bezos and the Enquirer went public. Trump misspelled "Bezos" as "Bozo" in his tweet.

Trump also took the opportunity to take a shot at the Post: "Hopefully the paper will soon be placed in better & more responsible hands!" The Saudi government has denied having anything to do with the National Enquirer's reporting.

(With input from Reuters)