Japan issues warning to Obama over 'comfort women' debate

Japan warned the issue of its wartime system of sex slavery was not a "diplomatic" subject, after US President Barack Obama on Friday called it a "terrible" violation of human rights.

Katsunobu Kato, deputy chief cabinet secretary, said Japan was aware of the suffering of the victims and was trying to avoid politicising the emotional issue.

"Prime Minister Shinzo Abe has said he is deeply pained to think of the people who experienced immeasurable pain and suffering," Kato said in a television programme late on Friday.

"This issue should not be made into a political or diplomatic subject."

In South Korea on Friday, Obama called for an accounting of the wrongs perpetrated by Japanese troops before and during the second world war when thousands of women were forced into prostitution, many from the Korean peninsula.

"This was a terrible, egregious violation of human rights. Those women were violated in ways that, even in the midst of war, were shocking," he said.