TOKYO (AFP) - Japan's Olympic committee on Wednesday announced its own probe of S$2.8 million allegedly paid to secure the 2020 Olympics - some of which was used to buy luxury watches, according to French investigators.

The JOC will set up a special team to look into the payments, which are already being investigated by French prosecutors and have been linked to a son of disgraced former world athletics chief Lamine Diack.

Allegations the payments were improper, first reported by Britain's Guardian newspaper last week, have rocked Japan, which beat Istanbul and Madrid in the race to host the Summer Games in 2013.

The JOC sent the money in two tranches to the now-defunct, Singapore-based Black Tidings company, either side of the International Olympic Committee vote which awarded Tokyo the 2020 Games.

Diack, whose son Papa Massata Diack has denied receiving the money, was an IOC member at the time.

Both men already face corruption charges in France related to the alleged cover-up of Russian doping cases.

"We decided to launch an investigation team, including outside lawyers, to probe whether there was illegality in the (consultants') contract," JOC president Tsunekazu Takeda, who led Tokyo's bid, told lawmakers during a third straight day of questioning in parliament.

Takeda said the JOC probe will involve "hearings from former officials of the bid committee", which dissolved after it landed the right to host the Games.

On Tuesday, Takeda refused to disclose details of the consultancy contract to lawmakers, citing a "confidentiality obligation".

Japanese officials, while acknowledging the money was paid, have denied wrongdoing and stress that the money was for consulting services related to the bid.

French prosecutors said last week that they suspect the S$2.8 million was intended to help secure the 2020 Olympics.