DUBAI, United Arab Emirates (AP) — The cellphone of Amazon founder and Washington Post owner Jeff Bezos was hacked in what appeared to be an attempt by Saudi Arabia’s crown prince to “influence, if not silence” the newspaper’s reporting on the kingdom, two U.N. human rights experts said Wednesday.

The U.N. experts called for an “immediate investigation” by the United States into a report commissioned by Bezos that showed the billionaire technology mogul’s phone was likely hacked after he received an MP4 video file sent from Crown Prince Mohammed bin Salman’s WhatsApp account after the two men exchanged phone numbers during a dinner in Los Angeles in 2018.

The video file was sent to Bezos’ phone five months before Saudi critic and Washington Post columnist Jamal Khashoggi was killed by Saudi government agents inside the Saudi consulate in Turkey in October. At the time, the crown prince was being widely hailed for ushering in major social reforms to the kingdom, but Khashoggi was writing columns in the Post that highlighted the darker side of Prince Mohammed’s simultaneous clampdown on dissent.

The Post was harshly critical of the Saudi government after Khashoggi’s killing and demanded accountability in a highly public campaign that ran in the paper for weeks after his death.

“The information we have received suggests the possible involvement of the Crown Prince in surveillance of Mr. Bezos, in an effort to influence, if not silence, The Washington Post’s reporting on Saudi Arabia,” the independent U.N. experts said.

At a time when Saudi Arabia was “supposedly investigating the killing of Mr. Khashoggi, and prosecuting those it deemed responsible, it was clandestinely waging a massive online campaign against Mr. Bezos and Amazon targeting him principally as the owner of The Washington Post,” the experts said.

Bezos first went public about the hack last year.

He said the National Enquirer tabloid, whose owner has ties to the crown prince, was threatening to publish Bezos’ private messages and photos if he didn’t stop a private investigation he’d sought into the hacking of his phone.

Iyad el-Baghdadi, an activist who worked with Bezos’ investigators, told The Associated Press it appears the hacking was about free speech. “It’s not about trying to compromise a businessman for business purposes,” he said. “It’s not about Amazon, it’s about The Washington Post.”

The Financial Times, which first reported on and reviewed the report commissioned by Bezos, noted the investigation “does not claim to have conclusive evidence,” and “could not ascertain what alleged spyware was used.”

Saudi Arabia’s foreign minister, Prince Faisal bin Farhan Al Saud, called the hacking allegations “absolutely illegitimate.”

“There was no information in there that’s relevant. There was no substantiation, there was no evidence,” he told an AP reporter at the World Economic Forum in Davos, Switzerland. “It was purely conjecture, and if there is real evidence, we look forward to seeing it.”