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Nissan and Mitsubishi have said Carlos Ghosn received "improper payments" totalling €7.8m ($8.9m; £6.9m) from a joint venture between the carmakers.

The claim follows a joint investigation by the companies into misconduct carried out by Mr Ghosn.

Mr Ghosn, former chairman of both firms, has been detained since November on charges involving financial crimes.

Both companies sacked him after his arrest last year. He denies any wrongdoing.

In a statement, Nissan said Mr Ghosn was compensated by the Netherlands-based joint venture, but he signed the contract without consulting two other board members, Nissan chief executive Hiroto Saikawa and Mitsubishi chief executive Osamu Masuko.

Mr Ghosn received compensation totalling €7.8m, according to the statement.

"Nissan views the payments Ghosn received from [the joint venture company] to be the result of misconduct and will consider measures to recover from Ghosn the full sum," it said.

Why is Mr Ghosn in detention?

Mr Ghosn has been charged with financial misconduct and breach of trust.

The 64-year-old is accused of having understated his pay for eight years and of having shifted private investment losses temporarily onto Nissan.

His lengthy detention in Japan without trial has drawn criticism and raised suspicion of a power play within an alliance between the two Japanese carmakers and Renault.

The Brazilian-born executive was the architect of the Renault-Nissan alliance and brought Mitsubishi on board in 2016.

Renault, in which the French government has a 15% stake, kept him on as chairman and chief executive even after his arrest in November.

But there is speculation it could replace him as a boss with expectation of a board meeting as soon as this weekend.

Renault was seen as the dominant partner because of its 43% shareholding in Nissan, despite selling fewer vehicles. Nissan's shareholding in Renault is only 15%.