U.N. Secretary-General Ban Ki-moon addressed members of the U.N. General Assembly, reminding them of their obligation to uphold the doctrine of the responsibility to protect as outlined in 2005.
"The concept arose out of the brutal legacy of the 20th century and, in particular, the appalling instances in which the machinery of state was used for systematic slaughter of innocent civilians while the world, for the most part, stood by," he said.
The doctrine calls on member states to act when individual states fail to live up to their responsibilities under international law.
Ban said he, along with U.N. human rights leaders and members of the General Assembly, have "sounded the alarm" in crises ranging from Ivory Coast to the Democratic Republic of Congo and Libya.
Syria, he stressed, was a case in point.
"The (Security) Council's paralysis does the Syrian people harm," he said. "It also damages its own credibility and weakens a concept that was adopted with such hope and expectations."
Veto-wielding member states China and Russia have objected to draft resolutions on Syria presented to the Security Council. They said measures lack balance.
Both sides to the conflict in Syria are accused of war crimes, though a recent U.N. report says alleged crimes committed by Syrian forces are more severe than those from anti-government elements.