"This horrific attack is yet another example of how sexual violence undermines efforts to achieve and maintain stability in areas torn by conflict but striving for peace," Clinton said in a statement.
"The United States will do everything we can to work with the UN and the DRC government to hold the perpetrators of these acts accountable, and to create a safe environment for women, girls, and all civilians living in the eastern Congo," Clinton vowed.
The United Nations adopted a resolution last year recognizing the importance of preventing and responding to sexual violence as a tactic of war against civilians.
Clinton said it was now time for member nations to go beyond that with specific steps to protect civilians against sexual violence and prosecute those who commit such atrocities.
The United Nations has a peacekeeping force of nearly 20,000 members in Congo. A U.N. spokesman said the peacekeeping force only heard about the incident in the eastern province more than a week after it happened.
The world body said Secretary-General Ban Ki-moon was outraged by the attack and dispatched a top official to Congo on Tuesday. The United Nations did not spell out the precise mandate of the mission.