Volkswagen chief executive officer Matthias Mueller reportedly has sought to calm nerves at the automaker as disputes with labour leaders and allegations from former chairman Ferdinand Piech threatened to disrupt efforts to overcome its diesel-cheating scandal.

"You're all certainly as irritated as I am, because Volkswagen needs something totally different now: namely, concentration in order to cleanly emerge from the diesel crisis," Mueller said Monday in a letter to staff obtained by Bloomberg, in which he vowed to resolve the conflicts.

Bloomberg said Mueller was battling renewed internal tensions that emerged last week. A fresh spat with labour leaders at the namesake VW brand raised questions over a planned overhaul at the carmaker's biggest unit only three months after a landmark agreement to slash costs. Meanwhile, Piech rekindled accusations that top managers, including former CEO Martin Winterkorn, knew about rigged diesel engines months before the manufacturer admitted to it after reportedly being tipped off by Israel's spy agency.

"Some speculation recently had more in common with a bad film script than reality," Mueller told employees, adding that internal conflicts being aired in public creates "the fatal and wrong impression that people at VW work against each other and not with one another".

"I promise you: we as the group management board, and I personally, will do everything to solve conflicts constructively and save Volkswagen from harm," Mueller said in the letter seen by Bloomberg.