Japanese Prime Minister Shinzo Abe

The trio, made up of two lawyers and a certified public accountant but whose names have not yet revealed, will investigate a transaction from the Bid Committee totalling $2 million (£1.3 million/€1.7 million) which has allegedly-corrupt implications.

It is thought the payment was made in two installments in 2013 before Tokyo won the right to host the 2020 Olympics at the International Olympic Committee (IOC) Session in Buenos Aires.

Obama will become the first sitting US president to tour the site of the world's first nuclear bombing this Friday, accompanied by Japanese Prime Minister Shinzo Abe.

In an interview with Japanese national broadcaster NHK, Obama - who emphasised denuclearisation early in his term - said the reality is that leaders often have to make hard choices during times of conflict and no apologies would be included in brief remarks he is expected to make in the western Japanese city.