BBC News with Stewart Macintosh

With fighting intensifying in the Syrian capital Damascus, the latest diplomatic effort to strengthen United Nations sanctions against President Assad's government has failed. Russia and China again vetoed a UN Security Council resolution proposing further sanctions as Laura Trevelyan reports from New York.

The British-drafted resolution would have renewed the

mandate

of the UN monitoring mission in Syria and sought to impose sanctions against President Assad's government if it continued to use heavy weapons. All Western countries said this was the best way to increase pressure on Syria's rulers; Russia and China disagreed. Russia, a key ally of Damascus, said a resolution under Chapter 7 of the United Nations Charter could ultimately lead to military intervention in Syria.

The American ambassador at the UN, Susan Rice, said the US would now work outside the UN Security Council to

bring pressure on

the Syrian government. In Damascus, Syrian government troops launched

sustained

assaults on rebels as President Assad appeared on television for the first time since the bombing killed three of his inner circle on Wednesday. Syrian state television showed Mr Assad swearing in a new defense minister while his forces used tanks, heavy artillery and helicopter gunships against opposition fighters. Rebel sources reported many casualties.

Syrian opposition fighters have seized border crossings with Iraq and Turkey as Jim Muir reports from neighboring Lebanon.