One of Japan’s leading politicians has poisoned already toxic relations with China and South Korea by saying that wartime sex slaves were a necessary evil.

Toru Hashimoto, who is Mayor of Osaka and co-leader of the right-wing Japan Restoration Party, also said “hot-blooded” US soldiers should use more prostitutes.

“Soldiers are put in extreme situations in which they can lose their lives,” he told the US military commander in Okinawa, Japan’s southernmost prefecture and home to 75 per cent of US bases in the country. “They are overflowing with energy. We have to think about the way they can let it out somewhere.”

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Mr Hashimoto, 43, told Japanese reporters that when he made the suggestion earlier this month, the commander “appeared frozen, smiled wryly and said it is banned”.

A Pentagon spokesman later called the Japanese politician’s suggestion “ridiculous”.

Mr Hashimoto is tipped as a future prime minister, despite a string of controversial bon mots. In 2011 he said Japan needed a dictatorship.

Speaking today, he again denied Japan forcibly rounded up Asian woman as sex slaves. Historians widely agree Japan’s military may have enslaved up to 200,000 Asian women during the Second World War, mainly from China and Korea.

Japanese nationalists argue the women were prostitutes who were recruited voluntarily from local communities.

South Korea reacted strongly to Mr Hashimoto’s comments, saying Japan should “stop distorting history” and “contemplate the pain and suffering it brought to its neighbours”.