U.N. High Commissioner for Human Rights Navi Pillay said from Geneva there was no end in sight to the conflict in Syria and no solutions "within easy grasp."
U.N.-Arab League envoy to Syria Lakhdar Brahimi, during a tour of the Middle East, has called for a temporary cease-fire in Syria to honor the three-day Muslim holiday of Eid al-Adha, which begins Oct. 26.
Civil war in Syria, which began in March 2011, has left an estimated 20,000 people dead.
Pillay, in her address, said the international community "cannot simply shrug and turn away" from the ongoing bloodshed.
Iranian and Turkish leaders this week spoke in favor of some form of truce in Syria. Members of the Security Council, however, have been unable to pass a formal resolution on the crisis. Veto-wielding members Russia and China said draft resolutions lack balance.
"I urge the Security Council to speak with one voice," said Pillay. "The longer this vicious conflict continues, the more lethal it becomes not just for Syria's own long-term future, but also for the entire region."
Turkish forces have responded to incidents along the shared border with Syria. Beirut has said Syrian forces on occasion have strayed across their border.