WASHINGTON (AP) — With their destination and mission among America’s closest guarded secrets, the small group of officials hand-picked by President Barack Obama boarded a military plane in March.

The travel plans of the U.S. diplomats and foreign policy advisers were not on any public itineraries. No reception greeted them as they landed. But awaiting the Americans in the remote and ancient Gulf sultanate of Oman was the reason for all the secrecy: a delegation of Iranians ready to meet them.