Secret US-Iran talks cleared way for historic nuclear deal The United States began a tentative outreach shortly after Mr Obama's inauguration in January 2009. Mr Obama and Iran's supreme leader, Ayatollah Ali Khamenei, exchanged letters, but the engagement yielded no results. In the end, it was efforts to win the release of three American hikers who had strayed across the Iranian border which led to the clandestine diplomacy. Oman's Sultan Qaboos was a key player, facilitating the release of the hikers in late 2010 and 2011 and then offering himself as a mediator for a US-Iran rapprochement. The secret informal discussions between mid-level officials in Washington and Tehran began. Oman's Sultan Qaboos The early contacts were exploratory discussions, officials said. They included exchanges between then US Ambassador to the United Nations Susan Rice, now Mr Obama's national security adviser, and Iran's envoy to the world body. The talks took on added weight eight months ago, when Mr Obama dispatched Mr Burns, Mr Sullivan and five other officials to meet with their Iranian counterparts in the Omani capital of Muscat. The senior administration officials who spoke to the AP characterised the Iranian attendees as career diplomats, national security aides and experts on the nuclear issue who were likely to remain key players even after the country's elections in the summer. Secretary of State John Kerry then visited Oman in May on a trip ostensibly to push a military deal with the sultanate but secretly focused on maintaining that country's key mediation role, particularly after the Iranian election in June, the officials said. Secretary of State John Kerry (REUTERS) Mr Rouhani's election on a platform of easing sanctions crippling Iran's economy and stated willingness to engage with the West gave a new spark to the US effort, the officials said. Two secret meetings were organised immediately after Mr Rouhani took office in August, and another pair of meetings took place in October. Mr Burns and Mr Sullivan led the US delegation at each of those sessions, and were joined at the final meeting by chief US nuclear negotiator Wendy Sherman. It was at the last secret gatherings - shortly after September's historic phone call between Mr Obama and Mr Rouhani following the UN General Assembly - that the deal began to take its final shape. At this month's formal talks in Geneva, Mr Burns and Mr Sullivan showed up as well, but the State Department went to great lengths to conceal their involvement, leaving their names off of the official delegation list. They were housed at a different hotel than the rest of the team, used back entrances to come and go from meeting venues and were whisked into negotiating sessions from service elevators or unused corridors only after photographers left.