German government ministers reportedly turned a blind eye to Volkswagen installing cheat devices to fool U.S. diesel emissions tests, raising the possibility that the mushrooming scandal could cause embarrassment for Chancellor Angela Merkel.

Britain's Daily Telegraph, citing a German parliamentary answer, reports that German ministers were warned months ago of "defeat device" software installed on Volkswagen’s diesel cars. The transport ministry answered a parliamentary question about the country's car industry on July 28 saying, "The federal government is award of (defeat devices), which have the goal of (test) cycle detection," according to The Telegraph.

The paper reported that while the government's statement did not specifically mention Volkswagen, the question that precipitated it, from a member of the country's Green Party, implied that the carmaker engaged in such practices.

“The government told us in July that it knew about this software, which has been used in the U.S.A.,” Green Party Deputy Leader Oliver Krischer told Germany's N24 television Wednesday. “It’s clear they knew the software was widely in use."

Meanwhile, Reuters reported that Volkswagen sent recall letters to California owners of its diesel-powered cars this past April, telling them to take their cars to a dealer for new software that the company said would ensure emissions were "optimized and operating efficiently."

Reuters reported that the company had sent the letters in an effort to fend off suspicious U.S. regulators who investigating discrepancies between the company's laboratory emissions test results and the amount of real-world pollution emitted by the cars. 

The California Air Resources Board (CARB) confirmed to Reuters that the letters were part of a voluntary recall that the state agency, the EPA, and Volkswagen had agreed to in December of last year. At the time, the car maker insisted that the discrepancy stemmed from a simple technical glitch. 

"This is one of the fixes they presented to us as a potential solution."  CARB spokesman Dave Clegern told Reuters. "It didn't work."

Volkswagen CEO Martin Winterkorn resigned on Wednesday under intense pressure following the EPA's disclosure Friday that stealth software makes VW's 2009-2015 model cars powered by 2.0-liter diesel engines run cleaner during emissions tests than in actual driving. The EPA has said that Volkswagen could be subject to fines of as much as $18 billion.

Early Thursday, member of Volkswagen's supervisory board said he expected further resignations at the German automaker. 

Olaf Lies, economy and transport minister of VW's home state Lower-Saxony, which holds a 20 percent stake in the company, told rbb-Inforadio Thursday that "there must be people responsible for allowing the manipulation of emission levels to happen."

The EPA accused VW of installing the so-called "defeat device" in 482,000 cars sold in the U.S. VW later acknowledged that similar software exists in 11 million diesel cars worldwide and was setting aside 6.5 billion euros to cover the costs of the scandal.

“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,” Winterkorn said in an announcement. “I am doing this in the interests of the company even though I am not aware of any wrongdoing on my part.”

The U.S. Justice Department has opened a criminal investigation into the scandal, while Other governments from Europe to South Korea have begun their own inquiries, and law firms have already filed class-action suits on behalf of customers. Volkswagen revealed plans on Wednesday to voluntarily submit a complaint to the state prosecutors’ office in Brunswick, Germany. Late Wednesday, VW filed a criminal complaint with German prosecutors seeking to identify those responsible for any illegal actions in connection with the scandal.

For the U.S. market, Volkswagen has yet to reveal a plan to fix its vehicles. The company has said it is working to “eliminate these (emissions) deviations through technical measures."

The Associated Press contributed to this report.

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