In September 2005, at the United Nations World Summit, all Member States formally accepted the responsibility of each State to protect its population from genocide, war crimes, ethnic cleansing and crimes against humanity. At the Summit, world leaders also agreed that when any State fails to meet that responsibility, all States (the “international community") are responsible for helping to protect peoples threatened with such crimes and that they should first use diplomatic, humanitarian and other peaceful methods. Then, if such methods are inadequate and if national authorities are “manifestly failing” to protect their populations, they should act collectively in a “timely and decisive manner” -- through the UN Security Council and in accordance with the Charter of the UN -- by using force.
The World Summit Outcome Document further stresses the “need for the General Assembly to continue consideration of the responsibility to protect”.
From - http://www.un.org/preventgenoc...responsibility.shtml