Britain has urged Iran's new president to set his country on a "different course" after years of deadlock and dispute with the West.
Hasan Rowhani, widely seen as the most moderate of the six candidates, was declared victor in the contest to succeed the unpredictable hardliner, Mahmoud Ahmadinejad.
The Foreign Office said in a statement that it hoped Mr Rowhani would use his victory to engage with international concerns over Iran's nuclear programme and develop a "constructive" relationship with the wider international community.
"We note the announcement that Hassan Rouhani has won the Iranian presidential elections," the statement said.
"We call on him to use the opportunity to set Iran on a different course for the future: addressing international concerns about Iran's nuclear programme, taking forward a constructive relationship with the international community, and improving the political and human rights situation for the people of Iran."