VIENNA, Austria - The United States and Europe have agreed on a compromise plan to accept expanded nuclear activities by Iran, but only if the enrichment process — a possible pathway to nuclear arms — is moved to Russia, senior officials and diplomats said Thursday. If accepted by Iran, the proposal could end a tug-of-war over whether to refer the Islamic republic to the U.N. Security Council for possible sanctions. The officials and diplomats, who demanded anonymity in exchange for discussing the strategy, said the plan would allow Iran to continue converting raw uranium into the gas that is spun...