BERLIN - German prosecutors say that automaker Volkswagen as a whole is responsible for the 2015 diesel emissions cheating scandal, a day after the company said it would accept a one-billion euro fine (US$1.18 billion).

Braunschweig senior prosecutor Klaus Ziehe said Thursday his investigation concluded the company failed to properly oversee its engine development department, but that the scandal cannot be attributed to a single department alone.

More than 10 million diesel vehicles were sold internationally with illegal emissions-controlling software.

Ziehe said the fine was "painful," adding it's the highest amount of money to be ever fined against a German company.

Prosecutors say the fine has to be paid within six weeks.

The scandal has already cost Volkswagen $20 billion in fines and civil settlements in the U.S.