"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," said Agnes Callamard, U.N. special rapporteur on summary executions and extrajudicial killings, and David Kaye, U.N. special rapporteur on freedom of expression.

The U.N. statement expressed concern not only about Saudi surveillance practices but also about a controversial Israeli firm, the NSO Group, that may have developed the malicious software to infiltrate the Amazon CEO's phone. The firm is already embroiled in a court battle with WhatsApp over an alleged cyberattack on its users.

A Saudi dissident also has filed a suit against NSO Group, saying it helped the Saudis carry out surveillance of Khashoggi prior to his October 2018 killing.

"This reported surveillance of Mr. Bezos, allegedly through software developed and marketed by a private company and transferred to a government without judicial control of its use, is, if true, a concrete example of the harms that result from the unconstrained marketing, sale and use of spyware," the U.N. experts said.

According to a technical report from the U.N., Bezos and bin Salman exchanged phone numbers connected to WhatsApp accounts in April of 2018, after Khashoggi had published several columns critical of the Saudi government.

The next month, the crown prince's account sent an encrypted video file to Bezos that could have been the vehicle for installing malicious code on Bezos' phone. Afterward, according the analysis, a massive amount of data transferred out of his phone.

The hack occurred around the same time that numerous other activists critical of the Saudi royal family had their phones hacked, according to the U.N. report.

Weeks after the hack, an online campaign emerged in Saudi Arabia that called for boycotting Amazon because of Bezos' ownership of the Post. Additionally, in early 2019, the National Enquirer reported that Bezos was having an affair with Lauren Sanchez and published photos of the two together. Afterward, Bezos' personal security consultant accused the Saudis of infiltrating the Amazon CEO's phone.

Asked about who conducted the report, a U.N. spokesperson referred POLITICO to a Financial Times story attributing the report to FTI Consulting. FTI Consulting declined to comment.

The Saudis denied involvement in the hack.

"Recent media reports that suggest the Kingdom is behind a hacking of Mr. Jeff Bezos' phone are absurd," the Saudi Embassy in the U.S. tweeted Tuesday evening. "We call for an investigation on these claims so that we can have all the facts out."

Amazon did not immediately respond to a request for comment.

Wednesday's U.N. statement has drawn congressional interest.

"To help Congress better understand what happened — and to help protect Americans against similar attacks — I encourage you to provide my office with information regarding your case," Sen. Ron Wyden (D-Ore.) wrote to Bezos.

"I am particularly interested in the technical details, including indicators of compromise from the hack, which could help the U.S. government, businesses and independent researchers discover who else might have been targeted and take steps to protect themselves," Wyden said, adding that he was interested in whether Bezos' security consultant also concluded that the crown prince's WhatsApp message was used to hack his phone.

