China's anti-monopoly regulators are looking at Toyota's luxury Lexus unit, the Japanese company has revealed, as an investigation into foreign automakers widens.

The company is "cooperating fully with the queries from the authorities on Lexus," said Toyota spokesman Naoki Sumino in Tokyo.

Authorities said last week that Audi and Chrysler would be punished for unspecified anti-monopoly violations. Mercedes-Benz, the luxury brand of Daimler AG, has said it is under scrutiny and a government spokesman said regulators are looking at 12 Japanese companies in the auto component industry.

Regulators have not disclosed the basis of their investigation. But customers complain prices of imported luxury vehicles and replacement parts are too expensive. Luxury cars in China can cost up to three times the price charged in the United States or Europe.

The headquarters in Japan of Nissan, owner of the Infiniti luxury brand, was unavailable for comment.

In an apparent effort to force down consumer prices, regulators have launched investigations of foreign auto, technology, pharmaceutical and dairy companies over the past two years using a 2008 anti-monopoly law.

The investigations are aimed at building a fair market, the China Association of Automobile Manufacturers (CAAM) said. "These moves were taken in accordance with the Anti-monopoly Law and are expected to clean up the auto market and safeguard the legal interests of Chinese consumers," it said.

Audi, Chrysler and Mercedes have announced pre-emptive price cuts of up to 38% for vehicles or replacement parts.

Yoko Suga, a spokesperson for major Japanese components supplier Denso, said: "We are not in a position to comment on anything related to any authorities' investigation."