Russia and China vetoed a Western-backed U.N. Security Council resolution on Thursday that threatened Syrian authorities with sanctions if they did not stop using heavy weapons against an uprising and withdraw troops from towns and cities. It was the third time that Russia, a key ally of the Syrian government, and China have used their veto power to block U.N. Security Council resolutions designed to put pressure on Syrian President Bashar al-Assad and halt the violence in the 16-month conflict that has killed thousands of people. The vetoed resolution, which would have extended a U.N. observer mission in Syria for 45 days, received 11 votes in favor, while South Africa and Pakistan abstained. Britain's U.N. Ambassador Mark Lyall Grant told the council he was "appalled" by Russia and China's vetoes. The effect of their actions is to protect a brutal regime. They have chosen to put their national interests ahead of the lives of millions of Syrians," he said. His French counterpart, Gerard Araud, said proponents of strong U.N. action on Syria would not be dissuaded. "We simply couldn't be accomplices of a strategy which brought together false diplomatic action and paralysis," Araud told the council. This double veto will not stop us. We will continue to assist a Syrian opposition on its path to democratic transition in Syria. The 15-member council still has time to negotiate another resolution on the fate of the unarmed mission before its initial 90-day mandate expires at midnight Friday (0400 GMT Saturday). More about: Syria, UN Security Council, United Nations