In Tehran, supporters of Ebrahim Raisi have been celebrating his election win.
But for Gulf Arab states working to improve ties with Iran, experts say the new president could mean a period of tougher talks.
The election of the hardline judge and cleric is a clear message, says UAE political analyst Abdulkhaleq Abdulla, that Iran is tilting to a more radical, more conservative position.
Analysts say much could hinge on Iran's revived talks on a 2015 nuclear deal.
Raisi - who is under U.S. sanctions - has voiced support for the negotiations which could lead to crippling U.S. sanctions being lifted.
On Sunday (June 20) negotiators for Iran and six world powers adjourned talks as remaining differences could not be easily overcome, according to Tehran's delegation chief.
Abbas Araqchi told Iranian state television that they were closer than ever to a deal but that bridging the gaps requires decisions to be taken by the United States.
Abdulaziz Sager, chairman of the Gulf Research Center, said having hardliners in power who are close to Supreme Leader Ayotallah Ali Khamenei could lead to an improved situation in the region - if there is success from the Vienna talks and an improved relationship with the U.S.
Since former U.S. president Donald Trump quit the deal in 2018, Iran has breached its strict limits on uranium enrichment.
But authorities have said moves would be reversed if the U.S. rescinds all sanctions.
President Joe Biden is seen as taking a more pragmatic Gulf approach but has demanded Iran rein in its missile program and end its support for proxies in the region including in Yemen.
Those are also key demands of Gulf Arab nations.
The United Arab Emirates and Oman have been swift to congratulate Raisi.
Saudi Arabia - which entered direct talks with Iran in April to contain tensions - and Bahrain are yet to comment.
But others are opposed to nuclear talks.
"Of all the people that Khamenei could have chosen, he chose the hangman of Tehran."
On Sunday Israeli Prime Minister Naftali Bennett described Raisi's election as "the last chance" for the world to see who they are dealing with, before returning to the nuclear agreement.