The timing wasn't great.

Just hours after the German auto industry took centre stage in a trade battle with the U.S.

German prosecutors widened an emissions cheating probe to include Audi's CEO.

Rupert Stadler has been added to the list of suspects accused of fraud and false advertising.

The move has triggered a leadership crisis at Audi and its parent Volkswagen.

In April Stadler was elevated to the post of head of sales for the entire group. (SOUNDBITE) (English) AUDI CEO, RUPERT STADLER, SAYING: "Product, product, product.

Technology and innovation.

And when it comes to digitalisation, you have to be at the forefront.

This is of course a very tough game." In 2015 Audi admitted its 3.0 litre V6 diesel engines were fitted with an emissions evading device deemed illegal in the United States.

Last month it also said it had discovered emissions-related problems with a further 60,000 cars.

It was a fresh setback to Volkswagen more than 2-1/2 years after it first admitted to cheating U.S. diesel exhaust tests.

Audi is the biggest contributor to Volkswagen's profit, It's shares fell more than one per cent on the news - so did rival Daimler's following a report that up to a million of its models contained illegal defeat devices. (SOUNDBITE) (German) HEAD OF CAPITAL MARKET ANALYSIS AT BAADER BANK, ROBERT HALVER, SAYING: "The German automobile industry is very important for Germany, it can't take another scandal, not a diesel scandal.

So it's good that Daimler's CEO is meeting with the German transport minister.

Anything to reduce this scandal is wonderful because with this trade war, the last thing we need is more disruption." Both auto firms says they're fully co-operating with the relevant investigators but declined to comment further.