PARIS (AFP) - Lawyers for French carmaker Renault have criticised their Japanese alliance partner Nissan for its handling of an internal probe into the Carlos Ghosn scandal, a Sunday newspaper has reported.

In a letter to Nissan dated January 19, the layers said they had "serious concerns about the methods used" by the company and its legal team, including the way they treated some Renault employees, according to France's Le Journal du Dimanche.

Former head of the alliance Ghosn is being held in Japan on charges he under-reported millions of dollars in pay as head of Nissan.

"Renault has gathered sufficient evidence to understand and regret the methods used by Nissan and its lawyers to seek interviews with Renault employees through the Japanese public prosecutor's office," they said.

Nissan was seeking "evidence to support allegations against Carlos Ghosn after his arrest" and failed to consult its French partner, according to the newspaper.

The firm also tried to search Ghosn's apartments in Brazil, Lebanon and the Netherlands without informing Renault, the letter added.

So far the French car giant has said its internal probe into its former boss has found his pay was in compliance with French law.

The executive's arrest in November has exposed rifts between Renault and Nissan, which some analysts say was bristling at Ghosn's efforts to bring the two automakers' operations even closer together.

Ghosn was the lynchpin of the three-way alliance, which also included Mitsubishi, earning industry plaudits for driving together a sometimes fractious threesome with headquarters 10,000km apart.

Much of the tension between the partners stems from a complex ownership structure that gives Renault 43 per cent of Nissan, whereas Nissan owns just 15 per cent stake in the French company - and no voting rights.