Russia and China cast a rare double veto at the U.N. Security Council on Tuesday to block a U.S.- and European-backed draft resolution condemning Syria for its brutal crackdown on protesters.

The veto marked a defeat after months of European-led diplomatic efforts to impose sanctions on Damascus for unleashing a violent response to the protests against President Bashar al-Assad. Syria’s U.N. ambassador, Bashar al-Jaafari, reacted to the veto with a smile and thanked the “voices of the wise” who had confronted what he characterized as colonial and military aspirations of Western powers that are “doomed to failure.”

The vote triggered an angry reaction from Susan E. Rice, the U.S. ambassador to the United Nations, who walked out of the Security Council meeting in protest during the Syrian envoy’s statement, in which he accused the United States of being a “party to genocide” through its support of Israel on the council. The British envoy, Mark Lyall Grant, walked out some time after Rice.

“The United States is outraged that this council has utterly failed to address an urgent moral challenge and a growing threat to regional peace and security,” Rice said, with unusual emotion. “Several members have sought for weeks to weaken and strip bare any text that would have defended the lives of innocent civilians from Assad’s brutality.”

France’s U.N. ambassador, Gerard Araud, vowed that this “veto will not stop us” from pressing for Syria to end a crackdown that has killed nearly 3,000 people. Rice said the council’s split provided a stark illustration of which countries support the aspirations of pro-democracy demonstrators in Syria and across the Arab world.

The draft garnered nine votes on the 15-member council, the minimum needed for adoption, as Brazil, India, Lebanon and South Africa expressed unease with the West’s push for sanctions by abstaining. The five permanent members each have a veto.

Speaking after the vote, Russia’s U.N. envoy, Vitaly I. Churkin, and China’s U.N. ambassador, Li Boadong, expressed concern that the resolution would have served to exacerbate tensions in Syria and could have served as a pretext for possible regime change there.

The clash comes weeks after the council agreed on a statement, generally considered less forceful than a resolution, condemning Syria’s conduct.

The council’s European members had initially pressed for a much tougher resolution, including an arms embargo. The watered-down draft blocked by Russia and China “strongly condemns the continued grave and systematic human rights violations by the Syrian authorities.” It accused the regime of carrying out “arbitrary executions,” torture and disappearances.

The draft demanded that Syria “cease the use of force against civilians,” release political prisoners and grant other “fundamental freedoms.” If Syria failed to comply, it said, the council would have to consider “other options,” a veiled reference to sanctions.