Tokyo Olympics 2020: French prosecutors probe '$2m payment'
French prosecutors are investigating a $2m (£1.4m) payment allegedly made to the son of the ex-world athletics chief and whether it was linked to Tokyo's bid for the 2020 Olympic Games.
Allegations of the sum allegedly paid to a firm linked to the son of Lamine Diack had appeared in the Guardian.
Both Lamine and his son, Papa Massata Diack, already face a corruption inquiry in France.
The Japanese government has insisted its Tokyo bid in 2013 was clean.
In March, French prosecutors had announced that an investigation into corruption in athletics was being widened to include the bidding and voting processes for the hosting of the 2016 and 2020 Olympics.
The latest development involves 2.8m Singapore dollars allegedly paid to a company based in the city state and linked to Papa Massata Diack.
A statement said the French "National Financial Prosecution service was informed of two financial movements alleged to have been carried out in July and October 2013".
The money was labelled as 'Tokyo 2020 Olympic Games Bid', coming from an account opened at a Japanese bank, for the profit of the 'Black Tidings' company in Singapore.
The statement added that payments "so close to the International Olympic Committee's designation of the organising city for the 2020 Olympic Games, important parallel purchases by Black Tidings in Paris", and other related issues had sparked a new inquiry.
Lamine Diack, 82, was formerly the president of the International Association of Athletics Federations (IAAF) and also a member of the International Olympic Committee (IOC).
He left the IOC soon after voting, in 2013, on whether Tokyo, Istanbul or Madrid should host the 2020 games.
He is now banned from leaving France pending the investigations.
Papa Massata Diack is believed to be in Senegal.
Last December, he told the BBC he and his father were innocent of the allegations against them.
Tokyo bid already being looked at
The Tokyo bid first came under scrutiny in January when the second part of a Wada (World Anti-Doping Agency) commission report into corruption included a footnote detailing a conversation between another of Lamine Diack's sons, Khalil, and Turkish officials heading up the Istanbul bid team.
A transcript of the conversation cited in the report suggested a "sponsorship" payment of between $4m and $5m (£2.8m and £3.4m) had been made by the Japanese bid team "either to the Diamond League (the annual series of track and field athletics meetings) or IAAF".
The footnote claims the Istanbul bid "lost Lamine Diack's support because they did not pay". Wada's independent commission said it did not investigate the claims "for it was not within our remit".
A Tokyo 2020 spokeswoman described the note in Wada's report as "beyond our understanding", adding that "Tokyo's bid was about Japan's commitment to address issues around the integrity of sport".
What is the background?
Lamine Diack is already being investigated by French authorities. He was arrested last year on corruption and money laundering charges, over allegations he took payments for deferring sanctions against Russian drugs cheats.
His son Papa Massata, who was employed by his father as a marketing consultant for the IAAF, is also under investigation, and a warrant for his arrest has been issued by Interpol.
Diack Jr has been banned for life by the IAAF.
The IOC overhauled its rules - and regained trust in the integrity of its bidding process - since the 1999 Salt Lake City bribery scandal exposed systematic corruption.
In February, Wada commission chief Dick Pound said he was "fairly certain" the IOC was free of organised corruption, but just a month later the French prosecutors opened their investigation into the bidding processes for 2016 and 2020.