The US House of Representatives on Monday approved a resolution urging Japan to "formally acknowledge, apologize and accept historical responsibility in a clear and unequivocal manner" for the suffering of "comfort women".

"Today, the House will send a message to the government of Japan that it should deliver an official, unequivocal, unambiguous apology for the indignity the comfort women suffered," said Michael M. Honda, a California Democrat who led the non-binding resolution.

Japanese Prime Minister Shinzo Abe, however, termed the resolution regrettable because the country had "already made amends".