The major United Nations powers last night agreed to offer Iran a stark choice of benefits or sanctions in the latest international gambit to persuade Teheran to abandon its nuclear ambitions.The initiative followed the failure of talks between the foreign ministers of Russia, China, France, Britain, America and Germany to resolve the deadlock on how to confront Iran. The "carrot or stick" plan came as US officials conceded that their hopes of pushing through this week a UN resolution mandating Iran's suspension of its nuclear enrichment programme were over. "I think the prospects for an agreement this week are not...