Sacked Nissan boss Carlos Ghosn has promised to "tell the truth" at a news conference next week.

He took to Twitter to announce his first briefing since being released on bail and hours after a report that prosecutors were preparing a fresh case against him. 

Ghosn was widely lauded for rescuing Nissan from the brink of bankruptcy two decades ago.

But he has experienced a dramatic fall from grace that shook the global auto industry and raised questions about the future of Nissan's alliance with France's Renault. 

He was arrested in Tokyo in November and faces charges of financial misconduct and aggravated breach of trust over allegedly failing to report around $82m in salary and temporarily transferring personal financial losses onto Nissan's books during the financial crisis. 

Released on $9m bail last month, Ghosn has denied the charges, calling them "meritless" and saying he was the victim of a boardroom coup. 

"I'm getting ready to tell the truth about what's happening. Press conference on Thursday, April 11," Ghosn tweeted from the @carlosghosn account on Twitter, which displayed the blue tick mark indicating it had been verified by the social media site. 

The account was created this month. It was the sole tweet, posted in Japanese and English. 

Under the terms of Ghosn's bail he is not allowed to use the internet, although the tweet may have been made on his behalf, as is common with celebrities and other high-profile figures. 

Earlier, Japan's Yomiuri newspaper reported that Tokyo prosecutors are preparing to build a fresh case against him over suspect payments the automaker made to a business partner in Oman.

Prosecutors are in discussions with the Supreme Public Prosecutors Office and others and plan to make a decision soon on whether to prosecute Ghosn on further charges of aggravated breach of trust, the newspaper said, citing sources involved in the case. 

A spokesman for the Tokyo prosecutors office said he was not aware of any new investigation when contacted by Reuters. 

Ghosn's spokesman has previously said payments of $32m made over nine years were rewards for the Oman firm being a top Nissan dealer. 

Such dealer incentives were not directed by Ghosn and the funds were not used to pay any personal debt, the spokesman said.