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.      

International mediator Kofi Annan voiced disappointment on Thursday at the failure of world powers to reach a common position on Syria.    

The Joint Special Envoy for Syria, Kofi Annan, is disappointed that at this critical stage the UN Security Council could not unite and take the strong and concerted action he had urged and hoped for. He believes that the voice of the Council is much more powerful when its Members act as one," his spokesman Ahmad Fawzi said in a statement issued in Geneva.          

The White House criticized the vetoes of Russia and China as "highly regrettable" and "highly unfortunate" and said it meant a U.N. observer mission there should not be extended.    

"They are on the wrong side of the Syrian people, the wrong side of hope for peace and stability in the region," White House spokesman Jay Carney told reporters after the vetoes were cast in New York. "It was a highly regrettable decision."    

He said Washington had made clear to the government of Assad that it would be "held accountable" if it uses chemical weapons against the opposition waging an uprising against him.       

UK Foreign Secretary Hague said the Russian and Chinese veto is “inexcusable and indefensible”.       

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.     

In turn, Russia said that the Western draft resolution would have paved the way for military intervention in Syria.      

Syrian state television aired footage on Thursday of Assad swearing in new defense minister Fahad Jassim al-Freij, the first images of the president since a bomb attack on Wednesday killed three senior official at a security meeting.       

Opposition sources and a Western diplomat earlier said that Assad is in the coastal city of Latakia, directing a response to the assassination of three of his top lieutenants.           

LBCI/REUTERS/AP