Secretary-General Ban Ki-moon called for international action against Syria on Thursday, saying President Bashar Assad has repeatedly broken promises to reform.
Using unusually strong language, Ban accused Assad of "escalating violence and repression" and ignoring appeals to stop, most recently by the Arab League.
"It's been almost six months. I have been speaking with him several times, and he made all these promises, but these promises have become now broken promises," Ban told a news conference.
If Assad's promises haven't been kept, the secretary-general said, "then enough is enough _ then (the) international community should really take some coherent measures and speak in one voice."
He said it's up to U.N. member states to decide what measures to take.
The Human Rights Council, the U.N.'s top human rights body, voted overwhelmingly last month to demand that Syria end its bloody crackdown and to cooperate with an international probe into possible crimes against humanity.
"We have to assess the violation of human rights which have happened during the ... very repressive handling of these demonstrations," Ban said.
After five months of deadlock, the U.N. Security Council finally responded to the escalating violence in a statement condemning Assad's forces for attacking civilians and committing human rights violations. But the Security Council remains divided over sanctions against Assad and his top supporters.
European nations and the U.S. circulated a draft U.N. Security Council resolution on Aug. 24 seeking an arms embargo and other sanctions aimed at stopping the Syrian government's ongoing crackdown on opposition protesters. That initiative faced immediate opposition from veto-wielding Russia, which introduced a rival resolution calling for Assad's government to halt the violence and expedite reforms.
It makes no mention of sanctions, which Russia and China have long opposed, and diplomats report no breakthrough in trying to reconcile the rival drafts.
Top French, British and U.S. officials have been trying to get Russian and Chinese leaders to agree to some sanctions, and those efforts are expected to continue during next week's ministerial meeting of the U.N. General Assembly.