Standard & Poor's Ratings Services downgraded Volkswagen AG's long-term rating by a notch to 'A-' from 'A'. The agency noted that CreditWatch was negative.

"The downgrade reflects our assessment that VW has demonstrated material deficiencies in its management and governance and general risk management framework. We believe VW's internal controls have been shown to be inadequate in preventing or identifying alleged illegal behaviour in the U.S. and misconduct in other regions," the agency said in its statement.