Tokyo 2020 boss tells Japan athletes don't 'mumble' anthem

The gaffe-prone 2020 Tokyo chief has warned Japan's Olympic team not to "mumble" the national anthem, saying those who can't sing it properly don't deserve to represent the country.

Former prime minister Yoshiro Mori, who heads up the committee for the 2020 Games hosted by Tokyo, was speaking at Sunday's send-off event for the 300 Japanese athletes heading to next month's Olympic Games in Rio de Janeiro.

"When you go up the podium, please do not be mumbling but sing the national anthem loudly," Mori said.

"Athletes who cannot sing the anthem should not be considered to be Japan's representatives," he added, according to the Asahi newspaper.

Mori turns 79 this month and served a short one-year stint as prime minister in 2000 to 2001, a tenure mostly remembered for a series of public blunders.

In 2014, he came under fire after criticising Japanese figure-skating heroine Mao Asada after a disappointing performance at the Sochi Olympics.

He also criticised Japan's ice dance pairing, Cathy and Chris Reed, saying: "They live in the US. We let them be part of the Japanese team because they are not good enough (to represent the United States)".