TEHRAN (Reuters) - Hardening its opposition to sanctions against Iran, Russia said on Friday the U.N. Security Council should only consider such measures if it had proof the Islamic Republic was trying to build nuclear weapons. The council is awaiting a report on April 28 from the Vienna-based International Atomic Energy Agency (IAEA) on whether Tehran is meeting its demands for a halt to uranium enrichment and answers to queries about its nuclear programme. The United States, Britain and France want the Security Council to weigh sanctions if, as widely expected, IAEA director Mohamed ElBaradei concludes Iran has not met...