President Hassan Rouhani called his landslide re-election a signal that Iranians want to continue their country's opening up to the world after decades of isolation.
"You said 'no' to those who wanted to stay still or go back in time," Rouhani said on Saturday, in his first speech to the nation since being declared the winner in Friday's presidential election.
The moderate reformer, who was came to office in 2013, said voters had sent a message that they want "peace over violence and tension" and "solidarity and unity over division."
Rouhani defeated by a wide margin his closest rival, hardliner Ebrahim Raisi, the Interior Ministry said.
Rouhani won 57 per cent of the ballots cast while Raisi earned 38 per cent, while 73 per cent of eligible voters turned out.
The poll was billed as a referendum on Rouhani's Western-friendly reformist agenda - in particular his nuclear deal with world powers, which set up international controls over Iran's nuclear programme in return for the end of economic sanctions.
More than 56 million Iranians were eligible to vote in the election, whose polling deadline was extended after huge voter turnout caused long queues at polling stations in the capital.
"Today the election is over and I am the president of the entire nation and need help from every single person - even those who were against my policies," Rouhani said.
Raisi, an arch-conservative who had the support of the state's powerful body of unelected Islamic clerics, had accused Rowhani of lies and incompetency, blaming him for high unemployment and saying that the Iran nuclear deal had brought nothing to the country.
Rouhani, 68, has told voters that they face a choice between freedom and "women and men separated by walls." Iran's presidential term is four years.
The two other candidates in the race received less than 5 percent of the vote.
EU foreign policy chief Federica Mogherini, who played a leading role in negotiating the nuclear accord in 2015, offered her congratulations to Rowhani for his "strong mandate."
She tweeted that the European Union is ready to work with Iran to secure the "full" implementation of the deal.
"His victory is a sign of the broad public support for the path of economic and political opening that Iran has taken since the nuclear deal. As a partner, Germany is ready to take this path further," German Foreign Minister Sigmar Gabriel said in statement.
So far the economic turnaround that Rouhani had promised with the nuclear deal has not materialized, with European banks refusing to finance new business agreements because a number of US sanctions against Iran remain in place.
Russian President Vladimir Putin and Syrian President Bashar al-Assad extended to their congratulations to Rouhani, with both expressing hope their security and economic ties with Tehran will deepen over the next four years.
Rouhani was elected president in August 2013, succeeding Mahmoud Ahmadinejad who held office for eight years.
Born in 1948 in Sorkheh in central Iran, Rowhani was for 20 years a member of parliament, serving as deputy speaker for eight years. He was appointed secretary of the Supreme National Security Council in 1989. In 2003, president Mohammad Khatami appointed him as chief nuclear negotiator.
With Rowhani in charge of the nuclear programme, the theocracy had its differences with the West, but there was neither a crisis nor crippling sanctions.
But Rowhani resigned shortly after Ahmadinejad's inauguration in the summer of 2005 because of various disagreements with the new president. Ahmadinejad went on to pursue a course of economic isolation and confrontation with the West over Iran's nuclear capabilities.
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