Japan has conveyed its concern to the U.S. government that a statement made by Secretary of State Rex Tillerson could contradict an agreement with South Korea over the "comfort women," sources close to the matter said.

Tokyo has told Washington that Tillerson's words could give the impression that the U.S. government has expressed an understanding of South Korea's stance. The U.S. side replied that it will take note of Japan's position, the sources said Saturday.

"It's one that only they can resolve," Tillerson told reporters this month after a 20-nation ministerial meeting in Vancouver, British Columbia. "And we know that there's more that needs to be done," he said, referring to the issue of the Korean girls and women who were forced into Japan's military brothels before and during the war.