Japanese advertising giant Dentsu Group and five other companies have been indicted over alleged bid-rigging of contracts for the Tokyo 2020 Olympics.

It comes after regulators filed criminal complaints against the firms and seven unnamed individuals.

The announcement follows months of investigations into alleged corruption in the planning and sponsorship of Olympics and Paralympics events.

Tokyo-based Dentsu is Japan's biggest advertising agency.

On Tuesday, Dentsu said in a statement that it "takes the situation seriously and offers its sincere apologies to its business partners, shareholders, and all other relevant parties for any inconvenience or concern this may cause."

The company added that a former employee of the group, who now works for one of its subsidiaries, had been indicted "for an alleged violation of the Antimonopoly Act in connection to the bidding for the test events of the Tokyo 2020 Olympic and Paralympic Games."

Another of the indicted firms, Hakuhodo DY Holdings, said an employee of its subsidiary, Hakuhodo DY Media Partners had been "indicted by the Tokyo District Public Prosecutor's Office based on charges brought by the commission."

"We also take this situation very seriously. The entire Hakuhodo DY group is committed to thorough compliance and to regaining the trust of society," it added.

The announcement came after the Japan Fair Trade Commission (FTC) filed complaints against Dentsu, Hakuhodo DY Holdings and four other advertising agencies.

"We determined that this is a malicious and serious case that will have a broad impact on people's lives," said Goh Okumura, an investigator at the FTC.

The other companies did not immediately respond to BBC requests for comment.

Last year, Haruyuki Takahashi, an ex-member of the Tokyo 2020 Olympics organising committee and previously an executive at Dentsu, was arrested on suspicion of receiving bribes from Olympic sponsors.

Mr Takahashi was accused of taking $380,000 (£315,600) in payments from high street business suit retailer Aoki Holdings, an official partner of the Tokyo 2020 games. Mr Takahashi has denied the allegations.

Officials also said that a former chairman and two other executives of Aoki Holdings had been arrested in connection with the case.

Tokyo was awarded the Games in 2013, beating Madrid and Istanbul.

(editor-in-charge：Press center6)