Iran's ambassador to Saudi Arabia arrived in Riyadh on Tuesday to take up his new post as the two countries rebuild ties following a seven-year diplomatic rift.
Alireza Enayati's arrival comes more than two months after Iran officially reopened its embassy and consulate in Saudi Arabia in June.
Mr Enayati told Iran's state news agency Irna before his departure that the Saudi ambassador to Iran was expected to arrive in Tehran later this week.
Hours later, Saudi Arabia’s ambassador to Iran Abdullah Al Anazi arrived in Tehran to begin his duties.
Saudi Foreign Minister Prince Faisal bin Farhan said the “resumption of work by the missions of the two countries, and the two ambassadors assuming their duties” was another step in developing relations between the two countries.
Iran and Saudi Arabia agreed in March to resume diplomatic and economic relations under a Chinese-brokered deal. Back-channel talks also involved Iraq, Jordan and Oman.
Prince Faisal said last month that the renewal of relations with Iran was a “turning point” for the region, with the kingdom keen to restore security and economic ties and to resume previous agreements with Tehran.
Saudi Arabia's Crown Prince Mohammed bin Salman met the visiting Iranian Foreign Minister Hossein Amirabdollahian last month, while King Salman has extended an invitation to Iranian President Ibrahim Raisi to visit the kingdom.
Mr Raisi has accepted the invitation and said he would visit “at the appropriate time”.
“We see such determination and seriousness on the Saudi side and we hope that Iran and Saudi Arabia, as two influential countries in the region, will be able to establish a successful model of co-operation in the region by working together,” Irna quoted Mr Enayati as saying after a meeting with Mr Raisi on Monday
As part of the thawing of relations, the Saudi and Iranian football federations have agreed that clubs from the two countries would be able to host home and away matches against each other, the Asian Football Confederation announced on Tuesday.
Relations between Saudi Arabia and Iran broke down in 2016, after Iranians stormed Saudi diplomatic missions in protest at Riyadh's execution of a Shiite cleric.