Volkswagen AG has accepted the resignation of Martin Winterkorn, its chief executive, who released a statement saying he was shocked and stunned by the revelation that the company's diesel vehicles included software to evade emissions standards.

The company's executive board has accepted Winterkorn's resignation, and said the top executive has no knowledge of the manipulation. In his Sept. 23 statement, Winterkorn also denied knowing about it.

"I am shocked by the events of the past few days," Winterkorn said. "Above all, I am stunned that misconduct on such a scale was possible in the Volkswagen Group. As CEO I accept responsibility for the irregularities that have been found in diesel engines and have therefore requested the Supervisory Board to agree on terminating my function as CEO of the Volkswagen Group. I am doing this in the interests of the company even though I am not aware of any wrong doing on my part."

On Sept. 18, the EPA accused Audi and Volkswagen of using a software algorithm in its four-cylinder diesels to circumvent federal emissions standards. The cars from the 2009 to 2015 model years could detect when the car is undergoing official emissions testing and turn on full emissions controls only during that test. This would violate the Clean Air Act.

The allegations cover about 482,000 models, including the Jetta TDI, Beetle TDI, Golf TDI, and Audi A3 TDI. The Passat TDI is affected from the 2014-MY and 2015-MY.

Volkswagen's executive committee has accepted Winterkorn's resignation and praised his contribution to the company. The board plans to make a recommendation about his replacement at its Sept. 25 board meeting.

"Winterkorn had no knowledge of the manipulation of emissions data," the board said in a Sept. 23 statement. "The executive committee has tremendous respect for his willingness to nevertheless assume responsibility and, in so doing, to send a strong signal both internally and externally. Winterkorn has made invaluable contributions to Volkswagen. The company's rise to global company is inextricably linked to his name."

Volkswagen is conducting an internal investigation in addition to federal and California probes. Those responsible "will be subject to the full consequences," the board said. The board has set up an ad hoc committee to determine the company's next steps. It added a criminal investigation may be necessary and submitted a complaint to the state prosecutor's office in Brunswick, Germany.

Winterkorn leaves the company at a time when it surpassed Toyota as the world's largest automaker for the first half of 2015.

"Volkswagen needs a fresh start — also in terms of personnel," Winterkorn said. "I am clearing the way for this fresh start with my resignation. The process of clarification and transparency must continue. This is the only way to win back trust. I am convinced that the Volkswagen Group and its team will overcome this grave crisis."