Volkswagen AG CEO Martin Winterkorn faced a grilling session before the company's board Wednesday over allegations of massive emissions tampering that have tarnished the image of the world’s largest carmaker.

On Tuesday, the company revealed that 11 million of its cars could have been affected, pulling the firm's market value by one-third and threatening the position of its CEO. 

The U.S. Environmental Protection Agency (EPA) accused Volkswagen and Audi Friday of using illegal software known as a “defeat device” to falsify the results of emissions regulation tests. Volkswagen reportedly admitted that it installed the defeat devices on about 482,000 vehicles.

The software covertly switches off pollution controls when the car is being driven, and reactivates them if it detects an emissions test. When the device is deactivated, the EPA said that emission levels of pollutant gases, including nitrogen oxide could reach as much as 40 times higher than standard limits.

"I am infinitely sorry that we have disappointed people's trust. I offer my deepest apologies," Winterkorn said in a statement. He added that the "irregularities ... contradict everything that our company stands for."

An unnamed source told Reuters Wednesday that the company was in a “tricky situation” regarding Winterkorn’s future, as the board did not yet know the full extent of his involvement in the scandal. Winterkorn is due to have his contract extended at the end of this week, and has shown no indication of intending to resign.

The news prompted an international outcry, with France calling for a Europe-wide probe into the allegations, and South Korea summoning company officials to discuss the allegations.

"We've called in Volkswagen representatives and engineers to the ministry for a meeting on Wednesday afternoon," South Korea's Environment Ministry Deputy Director Park Pan-Kyu told Agence France-Presse. He added that up to 59,000 cars in the country could have been equipped with the illicit software.

Volkswagen has halted the sales of all diesel vehicles in the U.S. following the revelations.

The EPA said the company could face fines of up to $18 billion for its conduct. The U.S. Justice Department has also launched a criminal probe, and several state attorney generals are forming an investigative group, New York Attorney General Eric Schneiderman said. “No company should be allowed to evade our environmental laws or promise consumers a fake bill of goods," he reportedly said in a statement.

The company’s stocks nosedived following the allegations, losing 17 percent of their value on Monday, and a further 20 percent on Tuesday. However, it was trading up 1.97 percent Wednesday, having made a modest rebound on the Frankfurt Stock Exchange, after almost $28 billion was wiped off the company’s market value this week.