The U.N. General Assembly is expected to approve Wednesday an Arab-backed resolution calling for a political transition in Syria and strongly condemning President Bashar Assad's regime for its escalating use of heavy weapons, U.N. diplomats said. But the resolution will not have as much support as the assembly's previous resolution last August denouncing Syria's crackdown on dissent, the diplomats said Tuesday, speaking on condition of anonymity because consultations have been private.

The United States and Britain stepped up pressure on Russia over Syria on Monday, but President Barack Obama warned old suspicions could trample new "common ground" on the crisis. Obama and British Prime Minister David Cameron sought to build momentum behind a new US-Russia sponsored conference on Syria, now expected to take place in June, as they met at the White House. "Syria's history is being written in the blood of her people, and it is happening on our watch," Cameron said. "The world urgently needs to come together to bring the killing to an end."

By Khaled Yacoub Oweis AMMAN (Reuters) - Syria's opposition coalition will meet in Istanbul on May 23 to decide whether to participate in a U.S. and Russian-sponsored conference to try to end the Syrian civil war, coalition officials said on Sunday.

Syria, which has been rocked by a revolt against the rule of President Bashar al-Assad since March 2011, has close links with Russia, an ally since Soviet times from which it buys most of its arms. Moscow has drawn Western criticism for its dogged support for the Damascus government even as the death toll has risen to more than 70,000. Following is a timeline of key developments: -- 2011 -- - April 27: Russia and China block a declaration submitted by Western countries at the UN condemning repression of peaceful protests by Assad's government.