Tunis - Veteran politician Beji Caid Essibsi pledged Monday to be a "president for all Tunisians," hours after the election commission confirmed his victory in Tunisia's first free presidential vote.
In a televised address, the 88-year-old said his win placed a "heavy burden on me. I am willing to shoulder this responsibility".
He called on Tunisians to "look forward to the future" after almost four years of turbulent transition.
Essibsi won Sunday's presidential run-off with 56% of valid ballots, while his rival, sitting President Moncef Marzouki, had 44%, the election commission said, citing initial results.
Final results are expected by 28 December.
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Marzouki, a human rights advocate, congratulated Essibsi in a phone call.
Marzouki called for shunning "all forms of violence and incitement" after his backers took to the streets in some towns to protest the election results.
In the southern town of El Hamma, police used tear gas to disperse dozens of Marzouki supporters, who burned car tyres and blocked roads, witnesses said.
The Interior Ministry, which is in charge of security in Tunisia, accused the protesters in El Hamma of setting local police facilities on fire.
Marzouki said he would not contest the outcome of the vote, Tunisia's official news agency reported, clearing the way for a smooth transfer of power.
The elections complete Tunisia's democratic transition after the ouster of longtime autocrat Zine El Abidine Ben Ali in a 2011 uprising.
Essibsi, a former prime minister, was ahead in last month's first round, when he garnered 39.5% of the vote compared with Marzouki's 33.4%.
In his presidential campaign, Essibsi pledged to bring stability to Tunisia.
His secularist Nida Tounes party took the lead in October's parliamentary elections, while the once-dominant Islamist Ennahada movement finished second.
Essibsi served in several high-ranking positions under the founder of independent Tunisia, Habib Bourguiba, and his successor, Ben Ali.
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US President Barack Obama congratulated Essebsi on his victory and praised the elections as "a vital step toward the completion of Tunisia's momentous transition to democracy."
European Union foreign policy chief Federica Mogherini hailed a "historic chapter" in the story of Tunisian democracy.
Egyptian President Abdel-Fattah al-Sissi congratulated Essibsi, expressing hopes for closer ties with Tunisia.
Last year, al-Sissi, the then-army chief, led the military's toppling of Islamist president Mohammad Morsi following mass protests against his one-year rule.
Tunisia, birthplace of the Arab Spring revolts, is widely seen as the sole success story of the Arab revolutionary movements.
Uprisings in Libya, Syria and Yemen have all led to conflicts.