VANCOUVER — U.S. Secretary of State Rex Tillerson urged Japan and South Korea on Tuesday not to let bilateral disputes over so-called comfort women affect trilateral security cooperation in addressing North Korea’s nuclear and missile programs.

“Our role has been simply to encourage them to deal with the issue, to not let that issue stand in the way of the greater security threats that are common to all of us,” Tillerson told reporters after a 20-nation ministerial meeting on North Korea in Vancouver, Canada.

Tillerson said the issue of Korean women forced into Japan’s wartime military brothels has so far “not been an obstacle” in strengthening three-way security cooperation.

The Secretary of State said the issue is not easy for the key U.S. allies to deal with, but that he hopes “ultimately they can move beyond that.”

“It’s one that only they can resolve,” he said. “And we know that there’s more that needs to be done.”

South Korea has reignited tension with Japan by requesting that the Japanese government take additional measures for former comfort women despite a 2015 bilateral agreement to “finally and irreversibly” resolve the protracted row.