Three U.S. senators formally asked President Barack Obama this week to redouble efforts to address the issue of Japan's sexual enslavement of Korean and other Asian women during World War II, saying it is a stumbling block to strengthening trilateral security cooperation.

In a letter sent to the White House Wednesday and made public the next day, Tim Johnson (D-SD), Martin Heinrich (D-NM) and Mark Begich (D-AK) noted the president's remarks on Japan's past atrocities during his latest trip to Asia in April.

Obama described what happened to the "comfort women" as a "terrible and egregious violation of human rights."

The senators said, "We affirm your statement that the 'women were violated in ways that even in the midst of war was shocking. They deserved to be heard, they deserved to be respected."

The senators added, "To this end, we wish to respectfully request you and your Administration's continued interest in this important issue."

They stressed resolving the matter will be key to fostering a closer trilateral relationship with South Korea and Japan amid Washington's push for rebalancing toward the Asia-Pacific region.

Their move is meaningful in that it represents the first formal activity in the Senate regarding the comfort women issue, a South Korean embassy official said on background.

Members of the House have been relatively active in dealing with the matter.

In 2007, the House adopted a resolution calling on Japan to offer an apology for enforcing tens of thousands of women into sexual slavery.

In January, it passed a spending bill with a related document attached, which calls for the secretary of state to pay more attention to the issue. (Yonhap)