According to ESPN, FIBA ruled Ogwumike, a former Women's National Basketball Association (WNBA) Most Valuable Player (MVP), and Williams had played for the US for too long to switch allegiance.

Players are not typically allowed to change their national team after they turn 17.

The two players, who have Nigerian passports, are facing a race against time to be cleared to play for Nigeria at the delayed Olympic Games here as the registration deadline is tomorrow.

ESPN reported Ogwumike and Williams have been given consent to compete for Nigeria from USA Basketball as they had paid an administration fee of $10,000 (£7,300/€8,500).

"We do tacitly believe there are undercurrents and motivation for such a decision which is repugnant to natural justice, equity and good conscience," the Nigerian Basketball Federation wrote in a letter to FIBA.

"It is also out rightly discriminatory because players of African descent are approved to play for other countries constantly but the reverse is not the case."

Los Angeles Sparks' Ogwumike, the WNBA champion and MVP in 2016 has won two World Cups and a Summer Universiade title with the US.

Williams has three gold medals for the US having been part of the American teams which won the Under-16 and 17 World Championship in 2009 and 2010, and the 2011 Under-18 and Under-19 event in Chile.

Nigeria are due to face the US in Group B of the women's basketball event at Tokyo 2020, along with hosts Japan and France.

The women's tournament at the Games, set to open here next Friday (July 23), is scheduled to run from July 26 to August 8.