“The inspections are related to Commission concerns that several German car manufacturers may have violated EU antitrust rules that prohibit cartels and restrictive business practices,” the commission, the bloc's executive arm, said in a statement.

It did not say which car companies were targeted, which is customary in EU anti-trust proceedings.

However, Volkswagen and Daimler both revealed separately they are under investigation.

Volkswagen said it was also a target of “ongoing antitrust investigations by the EU commission” while Mercedes-Benz maker Daimler confirmed an inspection and said it had “filed a leniency application.”

The raids are linked to a report in Der Spiegel that Volkswagen, Daimler and fellow German carmakers Audi, Porsche and BMW secretly worked together from the 1990s on car development, construction and logistics — including how to meet increasingly tough diesel emissions standards.

Both buyers and suppliers of the auto giants suffered from the under-the-table deals, the magazine alleged.

The allegations of antitrust violations are the latest cloud over Germany's auto industry.

In 2015, Volkswagen was forced to admit it had installed software in millions of its diesel vehicles to cheat emissions tests, which has already cost it tens of billions of euros.

In a separate cartel case, Daimler suffered a billion-euro fine from Brussels last summer for fixing truck prices with competitors.

In this latest case, Wolfsburg-based VW and Daimler were among the first to hand over details of the alleged broader collusion between the five firms to competition authorities, reported Spiegel, saying it had seen a relevant VW document.

BMW in July denied any collusion with industry rivals on emissions from its diesel engines, saying none of its models had been “manipulated” or violated industry regulations.