The surveillance claims, first reported by the Financial Times, were made by Hari Nada, 58, a senior adviser at Nissan, in a letter dated April 19 to the independent directors on the Japanese automaker's board.

Reuters, which has reviewed the letter, was the first to disclose its specific details. They relate to the surveillance claims, a stark split in senior management over Nissan's relationship with Renault and concerns about transfers of intellectual property to the French carmaker.

In the letter, Nada said Uchida had carried out surveillance over a long period. Nada said it was an effort to acquire leverage to remove an executive and board member who the Nissan chief executive regarded as an obstacle to reaching a new deal with alliance partner, Renault.

Gupta, appointed chief operating officer in 2019, had questioned the terms of the revised agreement Uchida is looking to finalise with Renault, according to Nada's letter and the four people with knowledge of the matter.

Asked to comment on the surveillance investigation, Nissan said in response to Reuters: "Independent third parties have been retained to verify facts and carry out appropriate actions."

Nissan declined any further comment on this story.

Reuters was unable to determine who was conducting the investigation for Nissan. It started in late May, one person with first-hand knowledge of the matter said.

Nada did not detail in the letter how he knew of the alleged surveillance of Gupta.

Reuters was unable to confirm independently that any surveillance had taken place.