Source: BBCNews
The South Korean government said that it will start an investigation into Volkswagen's (VW) diesel cars after the automaker admitted to rigging emissions tests in the US.
The government said it would test up to 5,000 VW Jetta and Golf cars, along with Audi A3s made in 2014 and 2015.
The probe will be expanded to all German diesel cars if issues are found.
VW shares plunged nearly 20% on Monday after US regulators found that some VW cars could manipulate emissions tests.
The Environmental Protection Agency (EPA) found that software in several diesel cars could deceive regulators.
Volkswagen was ordered to recall half a million cars in the US on Friday.
In addition to paying for the recall, VW faces fines that could add up to billions of dollars. There may also be criminal charges for VW executives.
The White House in Washington also reportedly said it was "quite concerned" about VW's conduct.
"It's clearly putting German industry under a very bad light," former VW employee Arndt Ellinghorst, now head of global automotive research at Evercore ISI told BBC News.
"This is just something that global consumers are not expecting from a German company, especially an automotive company who by the way is the biggest company in Europe."
Analysis: Richard Westcott, Transport Correspondent
There's one question people keep asking me at the moment. Is this the car industry's version of Libor, the scandal that rocked the financial world?
It's way too early to say just yet. But the pressure is now on the car industry to prove that cheating the pollution figures isn't a widespread problem stretching across both sides of the Atlantic.
The German government is investigating whether other companies are massaging their emissions data. The American regulator is widening its probe to other carmakers.
If they dig up more examples, the implications could be huge. Fines running into billions. A complete loss of credibility. And worst of all, the possibility that people have become ill or even died early because of higher emissions.
Americans don't tend to buy diesels. They represent just 3% of their car market. But half of all new cars sold in Europe are a diesel.
Chief apologises
Volkswagen chief executive Martin Winterkorn apologised after the scandal emerged and said he would "support" the German transport ministry's investigation into the carmaker.
"I personally am deeply sorry that we have broken the trust of our customers and the public," Mr. Winterkorn said.
He has launched an investigation into the software that allowed VW cars to emit less during tests than they would while driving normally.
The EPA found the "defeat device", the device that allowed VW cars to emit less during tests than they would while driving normally, in diesel cars including the Audi A3 and the VW Jetta, Beetle, Golf and Passat models.
VW has stopped selling the relevant diesel models in the US, where diesel cars account for about a quarter of sales.
The EPA said that the fine for each vehicle that did not comply with federal clean air rules would be up to $37,500 (£24,000). With 482,000 cars sold since 2008 involved in the allegations, it means the fines could reach $18bn.
That would be a considerable amount, even for the company that recently overtook Toyota to be the world's top-selling vehicle maker in the first six months of the year. Its stock market value is about €66bn ($75bn; £48bn).
Investigation
VW has ordered an external investigation, although it has not revealed who will be conducting it.
"We do not and will not tolerate violations of any kind of our internal rules or of the law," Mr Winterkorn said.
Arndt Ellinghorst explained why it is so difficult to sell diesel cars in the US: "Carmakers have to comply with 31mg NOx (nitrogen oxide) emissions per kilometre - in Europe that's 80mg, so it's much easier to comply in Europe when you're selling a diesel vehicle compared to the US."
"It makes cars far more expensive because carmakers have to add more technology."