WASHINGTON (AP) ― Japan’s main opposition party urged Tuesday against Tokyo revising an apology for Japan’s use of sex slaves during World War II.

Motohiro Oono, an upper house lawmaker of the Democratic Party of Japan, said it would be “counterproductive” to change a 1993 apology, known as the Kono statement, in which Japan expressed remorse for the suffering of so-called “comfort women.” Oono urged caution by new Prime Minister Shinzo Abe in his handling of historical issues.

Abe, whose conservative government took power after winning December elections, has previously advocated a revision of the statement that has been contested by rightists who deny that the “comfort women” were coerced by the military to be prostitutes.

Changing the apology would anger China and South Korea, which were both occupied by Japan for decades. Historians say up to 200,000 women, mainly from the Korean Peninsula and China, were forced to provide sex for Japanese soldiers in military brothels during the war.

“If the government revises the Kono statement on history, it is counterproductive in many senses,” Oono, who was vice defense minister in the previous government, told the Heritage Foundation think tank in Washington. “We would like to request Mr. Abe to have a cautious attitude,” he said, adding historical issues were best left to academics in the concerned countries.

The historical dispute adds to tensions over small islands that Japan contests with China and South Korea, and complicates efforts by Washington to foster security cooperation between its allies Japan and South Korea, in part to counter China’s growing assertiveness.