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Car giant Volkswagen says German prosecutors have expanded their probe of the emissions scandal to include the firm's chairman of the board.

Hans Dieter Poetsch was chief financial officer when the scandal over cars rigged to cheat on US diesel emissions tests broke in September 2015.

VW said prosecutors in Braunschweig were investigating two members of the board, Mr Poetsch and an unnamed other.

Former boss Martin Winterkorn is already being investigated.

In September, Matthias Mueller, the current chief executive, said the firm had made a "huge mistake" in using technology in its diesel cars to cheat on the tests.

He said the firm was working "constructively with the authorities in Germany, Europe and the United States".

The company also said VW and Mr Poetsch would "continue to give the inquiries by the public prosecutor's office their full support."

Mr Poetsch took over as chairman in October last year.

Software

On Sunday, VW said that "based on careful examination by internal and external legal experts", it reaffirmed its belief that board members had fulfilled their disclosure obligation under Germany's capital markets law.

The firm had installed software in diesel cars sold worldwide to detect when they were being tested, so the cars could cheat the results.

Some models could have been pumping out up to 40 times the legal limit of the pollutant, nitrogen oxide, regulators disclosed.

The carmaker said that around 11 million cars were affected worldwide.

The scandal has pulled down VW's global business and damaged its reputation.

It has also faced a flurry of lawsuits in the US and in other countries.