The US offices of three Japanese automotive parts suppliers to Toyota - Denso, Tokai Rika and Yazaki - were raided on Tuesday by the Detroit office of the FBI over allegations of price-fixing, media reports said.

"The antitrust division is investigating the possibility of anti-competitive cartel conduct of automotive electronic components suppliers," Department of Justice spokeswoman Gina Talamona told Dow Jones. "We are coordinating with the European Commission and other foreign competition authorities."

The department was looking at possible anti-competitive behaviour of these companies, not at the components themselves, a source told the news agency. Toyota has stakes in Denso and Tokai Rika. There was no connection between the investigation and Toyota's recall problems, the report added.

US-based auto parts makers have for years cited frustration in attempting to win new contracts from Toyota when bidding against one of Toyota's "captive suppliers", Dow Jones noted. Parts makers had speculated that Toyota always gave its partially owned suppliers preferred treatment.

Denso confirmed it was inspected by the FBI and said the investigation was based on allegations of violations of antitrust laws.

"We are fully cooperating with the investigation," a Denso spokeswoman told Dow Jones. Yazaki said authorities visited the company's North America headquarters in Canton, Mississippi, along with its Lexington, Kentucky, and Columbus, Ohio, facilities.

Canton is home to a Nissan plant and Lexington is the location of Toyota's first US assembly facility, opened some 20 years ago. It now has 10 vehicle plants in North America.

"Yazaki is fully cooperating with authorities," the company said in a statement. "At this point, we are not in a position to disclose any additional information as we have not been informed of the details of the investigation."

Washington-based Toyota public affairs spokeswoman Cindy Knight told Dow Jones the company was still trying to determine why the FBI is investigating Denso, Yazaki and Tokai Rika.

"Toyota is aware that certain suppliers have been contacted by government officials, but we have limited information about the scope of the investigation," Knight said. "Toyota has not been contacted by authorities."

Yazaki supplies electronic components while Denso makes a variety of parts including accelerator pedals that Toyota has used in its vehicles. Those pedals weren't involved in the recent recalls of Toyota vehicles based on complaints of unintended acceleration, the report noted.

Tokai Rika makes a variety of safety products including seat belts, door mirrors, power windows and steering switches.

Toyota Motor Engineering & Manufacturing North America (TEMA) said in a statement it had not been asked for information in connection with the investigation but would cooperate if asked.