In the wake of the US Environmental Protection Agency (EPA) accusing Volkswagen and Audi of using an illegal software, or a 'defeat device', for cheating emission regulation tests, many countries have expressed concern over VW vehicles sold in their country.

One of the biggest scandals in automobile world has prompted France to call for a Europe-wide probe into the accusation, while South Korea has summoned Volkswagen officials.

French Finance Minister Michel Sapin requested over French radio that it seemed necessary to check cars manufactured by other European carmakers also in order to reassure the public.

South Korea too has talked of adopting a tough stance.

"We will start conducting tests no later than next month," said a senior official at the South Korean environment ministry.

The problem with Volkswagen does not seem to end soon, as the US Justice Department has reportedly launching a criminal investigation.

Volkswagen, the world's largest automaker by sales, has fallen into deep trouble when the US EPA said Volkswagen intentionally violated the Clean Air Act by using sophisticated software in its diesel-powered cars that detects emission testing.

The software switches on all the emission control systems of a vehicle while the test is going on, and switches off in real-world driving conditions, resulting in emission levels of up to 40 times over the permitted limits. 

According to the EPA, the cars in question are four-cylinder Jetta, Beetle, Golf, Audi A3 manfactured between 2009 and 2014, and VW Passat built between 2014 and 2015.

Under the current federal law, the EPA can apply a maximum fine of $37,500 per car, which means Volkswagen and Audi could face a total fine of up to $18 billion.

The shares of Volkswagen plunged 18.6% on Tuesday as a result of the accusations against the company. Subsequently, VW Group CEO Martin Winterkorn has apologized for "breaking the trust of our customers and the public."