Tokyo prosecutors have indicted advertising giant Dentsu Group and five other Japanese firms and seven individuals for alleged bid-rigging related to the Tokyo Olympics and Paralympics.

The six companies indicted on Tuesday include Dentsu Group, second-largest ad firm Hakuhodo, Tokyu Agency and event producer Cerespo.

The seven people indicted include Mori Yasuo, ex-deputy director of the Tokyo Games' organizing committee's operation bureau, and former Dentsu Group executive Henmi Koji.

Three of them were indicted without arrest. They include the president of Hakuhodo DY Sports Marketing.

The prosecutors say the six companies and the seven individuals violated the anti-monopoly law by pre-arranging bid winners to plan and stage the Games' test events. The winners signed discretionary contracts to run actual competitions in the Games. The contracts reportedly totaled about 43.7 billion yen, or 320 million dollars.

The prosecutors suspect the firms had rigged bids for the test events with an eye on larger contracts for actual events.

The prosecutors suspect a group firm of major ad agency ADK was also involved in the rigging, but it has apparently been removed from the indictment list as it was the first to voluntarily report the wrongdoing to the Japan Fair Trade Commission.

The prosecutors have not disclosed whether the seven individuals have admitted to the allegations, but informed sources say Mori and Henmi have done so.

The investigation into the alleged bid-rigging began after suspected bribery incidents came to light.