ABOARD AIR FORCE ONE: The White House on Thursday criticized the vetoes of Russia and China of a U.N. Security Council sanctions resolution against Syria 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."

Carney, aboard Air Force One with President Barack Obama headed for Florida, also said the United States does not support extending the U.N. observer mission in Syria after the failure of the Western-backed U.N. resolution.

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