By Laila Bassam and Tom Miles BEIRUT/GENEVA (Reuters) - Russia's military intervention in the Syrian war has all but destroyed a deal agreed last month to halt fighting between warring sides in two areas of the west, unpicking a rare success for foreign-backed diplomacy in the four-year-long conflict. Implementation of the deal agreed with U.N. help to extricate rebels from the town of Zabadani and trapped villagers from al-Foua and Kefraya has effectively been shelved following Russian air strikes in support of President Bashar al-Assad, three sources familiar with the talks told Reuters. The deal brokered with Iranian and Turkish help followed a weeks-long offensive by the Syrian military and Shi'ite Islamist Hezbollah to capture the town of Zabadani near the Lebanese border from insurgents who are still holed up there.