UN Secretary-General Ban Ki-moon urged Iran to play a "constructive role" in regional and international affairs Saturday after Hassan Rowhani was declared president.
The moderate cleric's election ended eight years of conservative grip on the top office in a victory cheered in the streets and cautiously welcomed by world powers.
Ban "intends to remain engaged with the Iranian authorities and with the president-elect on issues of importance to the international community and the welfare of the Iranian people," his office said in a message congratulating Rowhani.
"He will continue encouraging Iran to play a constructive role in regional and international affairs."
Ban also expressed "satisfaction" at the reported high turnout of 72.7 percent of the electorate.
The United Nations and Western powers have slapped a range of sanctions on Iran in an attempt to dissuade Tehran from developing a nuclear weapon under the cover of a civilian nuclear energy program.
The Islamic republic has denied it is seeking the atomic bomb.
In his first statement after being declared outright winner with 50.68 percent of votes cast in Friday's vote, Rowhani called on world powers to treat Iran with respect and recognise its rights, in an apparent allusion to its controversial nuclear policy.
During the campaign, he had pledged to move to ease the sanctions, which have hit hard. Inflation is more than 30 percent, the rial has lost nearly 70 percent of its value and unemployment is rising.
Rowhani touts his relations with supreme leader Ayatollah Ali Khamenei, who has the final say on all key issues, including the nuclear program.