The California Air Resources Board (CARB) said VW's proposed fix was not adequate or fast enough, and that it would continue its investigation as well as talks with VW to find a fix.

"Today's announcement addresses the initial recall plans Volkswagen submitted to CARB in December," VW said in an emailed response to the announcement.

"We are committed to working cooperatively with CARB and other regulators, and we plan to continue our discussions tomorrow when we meet with the EPA."

(Reporting by Jan Schwartz and Christoph Steitz)