The wife of ex-Nissan chief Carlos Ghosn on Monday reached out to US President Donald Trump, asking him to press Japan at upcoming talks about "fair trial conditions".

Carlos Ghosn is awaiting trial in Japan over charges of under-reporting his salary for years while at Nissan and using company funds for personal expenses. The 65-year-old denies the accusations.

"World leaders are going to be meeting at the G20 at the end of the month," Carole Ghosn told the BBC in an interview broadcast on Monday.

"I'd like President Trump to speak to Prime Minister (Shinzo) Abe about fair conditions, fair trial conditions, and to let me speak to my husband -- and also to respect this presumption of innocence until proven guilty."

She added that the last time she saw her husband was on April 4 when prosecutors stormed their apartment in the early hours.

Carlos Ghosn, who is a French citizen, was freed in Japan on $4.5 million bail in April after being detained on fresh charges but is living under strict conditions including restrictions on seeing his wife.

Under those bail conditions, Ghosn must stay in Japan and live in a court-appointed residence with cameras to monitor his movements.

"I think all of this could have been dealt with internally within the company. This didn't need to go this far," Carole Ghosn added on Monday.

"On top of this, my husband is innocent and time will prove the truth."

This year's G20 summit will be held in the Japanese city of Osaka from June 28-29.