LAS VEGAS -- The top executive of the Volkswagen brand worldwide says he's optimistic U.S. environmental regulators will approve fixes within the coming weeks or months for diesel engines that cheat on emissions tests.

Brand CEO Herbert Diess said Tuesday night at the CES gadget show in Las Vegas the company is having constructive discussions with the U.S. Environmental Protection Agency and the California Air Resources Board.

But the EPA didn't sound as optimistic, issuing a statement Wednesday saying talks with VW so far "have not produced an acceptable way forward."

Diess said VW already has received approval to fix 8.5 million cheating cars in Europe.

Repairs will start this month, and most will be fixed this year.

But the U.S. cars are more problematic because they emit up to 40 times more toxic nitrogen oxide than allowed. Nearly 600,000 cars are affected in the U.S., with a total of 11 million worldwide.