The security chief for Jeff Bezos, chief executive of Amazon, says the Saudi government had access to Bezos’s phone and gained private information from it.

Gavin de Becker, Bezos’s longtime security consultant, said he had concluded his investigation into the publication in January of leaked text messages between Bezos and Lauren Sánchez, a former television anchor whom the US National Enquirer tabloid newspaper said Bezos was dating.

Shortly before their publication, Bezos had become the subject of tabloid stories after he and his wife MacKenzie, announced they were divorcing.

In February, Bezos accused the National Enquirer’s owner of trying to blackmail him with the threat of publishing “intimate text messages” he allegedly sent to Sanchez, unless he said in public that the tabloid’s reporting on him was not politically motivated.

In an article for The Daily Beast website, De Becker said the parent company of the National Enquirer, American Media Inc (AMI), had privately demanded De Becker deny finding any evidence of “electronic eavesdropping or hacking in their news-gathering process”.

“Our investigators and several experts concluded with high confidence that the Saudis had access to Bezos’ phone, and gained private information,” De Becker wrote. “As of today, it is unclear to what degree, if any, AMI was aware of the details.”

De Becker alleged Saudi Arabia has targeted the Washington Post, which is owned by Bezos, following the death last year in Turkey of Jamal Khashoggi, one of its columnists. Khashoggi, a Saudi national, was killed in the Saudi consulate in Istanbul in October.

“Some Americans will be surprised to learn that the Saudi government has been very intent on harming Jeff Bezos since last October, when the Post began its relentless coverage of Khashoggi’s murder,” De Becker wrote.

The CIA has concluded that Khashoggi’s murder was probably ordered by the powerful Saudi crown prince, Mohammed bin Salman.

AMI denied De Becker’s claims in a statement on Sunday. It said: “Despite the false and unsubstantiated claims of Mr De Becker, American Media has, and continues to, refute the unsubstantiated claims that the materials for our report were acquired with the help of anyone other than the single source who first brought them to us … there was no involvement by any other third party whatsoever.”

“The fact of the matter is, it was [Lauren Sanchez’s brother] Michael Sanchez who tipped the National Enquirer off to the affair on 10 September 2018, and over the course of four months provided all of the materials for our investigation.

“His continued efforts to discuss and falsely represent our reporting, and his role in it, has waived any source confidentiality.

The Saudi embassy in Washington has yet to comment on the latest allegations. In February, the kingdom’s minister of state for foreign affairs said Saudi Arabia had “absolutely nothing to do” with the National Enquirer’s reporting on the affair.

De Becker said he has turned over the findings of his investigation to US federal officials.

Reuters contributed to this report