WASHINGTON — U.S. regulators charged Volkswagen and former CEO Martin Winterkorn with defrauding investors during its massive diesel emissions scandal.

The surprise charges from the U.S. Securities and Exchange Commission come two years after the German automaker settled with the U.S. over criminal and civil charges.

The SEC said that between April 2014 and May 2015, Volkswagen issued more than $13 billion in bonds and asset-backed securities in U.S. markets when executives knew that more than 500,000 vehicles in the country grossly exceeded legal vehicle emissions limits.

Volkswagen made false and misleading statements to investors and underwriters about vehicle quality, environmental compliance, and the company’s financial standing, which gave Volkswagen a financial benefit when it issued securities at more attractive rates for the company, according to the SEC.

“Volkswagen hid its decade-long emissions scheme while it was selling billions of dollars of its bonds to investors at inflated prices,” said Stephanie Avakian, co-director of the SEC’s enforcement division.

In September 2015, Volkswagen installed software on more than 475,000 cars that enabled them to cheat on emissions tests, according to the Environmental Protection Agency. The software reduced nitrogen oxide emissions when the cars were placed on a test machine but allowed higher emissions and improved engine performance during driving.

In 2016, the Justice Department sued Volkswagen over the emissions-cheating software and the Federal Trade Commission sued the company for false claims in commercials promoting its “Clean Diesel” vehicles as environmentally friendly.

The company has paid some $20 billion in fines and civil settlements. It has also pleaded guilty to criminal charges in the United States.