The two-decade-old partnership of Renault SA and Nissan was plunged into fresh crisis this week after Renault signaled it would block its partner from adopting planned governance reforms unless the French automaker received more say in the new system. Nissan has publicly called that demand "most regrettable".

"I have to say that they are endangering the alliance. They have to be very careful not to antagonize Japanese people, shareholders," the person said, referring to Renault.

"Renault has been saying the alliance is important and irreversible but what they are trying to do is to break the alliance," the person said, declining to be identified because of the sensitivity of the issue.

(Reporting by Linda Sieg; Writing by David Dolan; Editing by Chang-Ran Kim)