Sultan Haitham of Oman was due to meet Iran's President Ebrahim Raisi in Tehran on Sunday for a two-day state visit.
The trip follows a diplomatic push by Muscat to broker the restoration of ties between Saudi Arabia and Iran.
The effort was announced by China on March 10 and has involved negotiations hosted by Iraq and Jordan.
Sultan Haitham's trip to Iran was reported by the state-run Oman News Agency on Sunday. Iranian media showed Sultan Haitham disembarking from a Royal Flight of Oman aircraft, one of seven government planes for royal use, and being greeted by officials, including Iran's Vice President Mohammad Mokhber Dezfuli.
Sultan Haitham is accompanied by a high-level government delegation including the head of the armed forces Vice Admiral Abdullah Bin Khamis Raisi, as well as the ministers of finance, commerce and defence, the Diwan of Royal Court said.
An official reception ceremony met Sultan Haitham "upon the arrival of His Majesty's convoy to the presidential building in the Saadabad Palace in the capital", Oman News Agency said.
Last week, Iran’s ambassador to Oman Ali Najafi Khoshroudi said the two countries were enjoying “an unprecedented level of partnership”.
“Both countries engage in fruitful discussions on economic and political matters that serve the best interests of their respective peoples,” he said.
“These improvements are expected to have a significant impact on boosting trade and economic exchange between Tehran and Muscat.”
In addition to mediating between Tehran and Riyadh, Oman has long been an interlocutor for the West with Iran and has helped secure the release of several foreign and dual citizens.
On Friday, Oman helped secure the release of a Belgian aid worker, who was arrested last year and sentenced to 40 years in prison and 74 lashes on charges including spying, in exchange for an Iranian diplomat sentenced to 20 years in prison in connection with a failed bomb plot in France.
