The attack also wounded at least 15 others
His Majesty Sultan Haitham bin Tarik of Oman arrived in Tehran on Sunday for a two-day visit.
His trip comes just two days after Tehran freed Belgian aid worker Olivier Vandecasteele from almost 15 months in custody in exchange for diplomat Assadollah Assadi, who was held in Belgium over a 2018 plot to bomb an Iranian opposition rally outside Paris.
The Gulf Sultanate helped facilitate the prisoner swap.
The sultan was greeted on arrival at Tehran's Mehrabad airport on Sunday by First Vice-President Mohammad Mokhber and later met President Ebrahim Raisi at the Sadabad palace in north Tehran.
Ahead of his visit, the newspaper Asharq Al Awsat quoted Omani Foreign Minister Sayyid Badr Hamad Al Busaidi as saying it comes "in pursuance of constructive cooperation and consultation about different issues on the regional and international arenas".
The Omani leader's visit comes a year after Raisi visited Muscat, and follows a China-brokered rapprochement deal between Saudi Arabia and Iran announced in March.
Busaidi said Oman was optimistic the sultan's "historic" trip to Iran would be "beneficial in regional and global terms".
Oman has close ties with Iran, and played a mediating role between Tehran and the United States in the build-up to a nuclear deal Iran and world powers reached in 2015.
The last visit by an Omani sultan to Iran was in 2013 when Qaboos bin Said Al Said visited Tehran during the presidency of Hassan Rouhani, who was in office when the 2015 deal was sealed.
Sultan Qaboos also maintained good ties with Tehran and acted as an intermediary between Western countries and Iran. — reuters
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