Moody's Investors Service Tuesday affirmed Volkswagen AG's (VW) issuer rating at 'A3'. The outlook is negative.

"VW's overall unit sales performance, particularly for its premium Audi and Porsche brands, have remained surprisingly strong and we expect the company's earnings and cash flow from operations to remain robust in 2016-17, supporting the rating," a Moody's Senior Credit Officer and lead analyst for Volkswagen, Yasmina Serghini, said.

She added that the agency expected VW to take steps to address internal control and governance issues.