A Tokyo Olympics executive has been arrested on suspicion of violating Japan's Anti-Monopoly Act. Sources say former deputy director of the Tokyo Olympics and Paralympics Organizing Committee's operations bureau Mori Yasuo has admitted to involvement in rigging bids for test events.

Prosecutors and Japan Fair Trade Commission officials suspect that the organizing committee colluded with Dentsu, the country's largest ad agency, to steer contracts to specific companies.

The arrest comes amid a probe into 26 bids held in 2018 for contracts to plan test events. Investigators say nine firms, including Dentsu, and one consortium won related contracts worth more than 500 million yen, or almost 4 million dollars.

Sources say explanatory documents prepared before the tender suggested that winning firms would also, in principle, receive orders for projects leading to the Games.

Also, investigators are believed to be looking into possible bid-rigging involving around 40 billion yen, or about 303 million dollars, in contracts related to operating the Games themselves as well.

They say winners of test-event bids signed discretionary contracts that included work for the actual Games.

Sources also say Dentsu officials have already admitted to rigging bids.

Separately, 15 people, including another former executive of the organizing committee, have been indicted in a bribery case related to the Tokyo Games.