Nissan's former chairman Carlos Ghosn has denied allegations of financial misconduct, claiming he had no intention of making false reports, Japanese media said on Sunday.

The Brazil-born tycoon, who has not spoken publicly since he was arrested last Monday, told prosecutors he did not intend to understate his income on financial reports, public broadcaster NHK said.

Without exercising his right to remain silent, Ghosn advocated his view to prosecutors, NHK said, quoting unnamed sources.

Ghosn was sacked as Nissan chairman Thursday, a spectacular fall from grace for the once-revered boss whose arrest and ouster have stunned the business world.

Prosecutors accuse Ghosn and fellow executive Greg Kelly of under-reporting the former chairman's income by around five billion yen ($44 million).

Kelly also denied the allegations, saying Ghosn's salaries were paid appropriately, news reports said.

Local media reported Sunday that Nissan had formed a “secret” team earlier this year to probe the alleged financial misconduct.

A small team involving Nissan's board members carried out its internal probe confidentially on concerns about possible destruction of evidence by Ghosn, Japan's Kyodo News reported, quoting unnamed sources.

Ghosn is being held custody in a Tokyo detention centre.

On Wednesday, prosecutors successfully applied to extend his custody for an additional 10 days as they stepped up their questioning.