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Emilio Morenatti, Associated Press
Prime Minister Recep Tayyip Erdogan, who is the front-runner in Turkey's presidential election, casts his vote at a polling station in Istanbul, Turkey, on Sunday, Aug. 10, 2014. Turks were voting in their first direct presidential election Sunday _ a watershed event in Turkey’s 91-year history, where the president was previously elected by Parliament. Prime Minister RecepTayyip Erdogan, who has dominated the country’s politics for the past decade, is the strong front-runner to replace the incumbent, Abdullah Gul, for a five-year term.

ISTANBUL — Turks voted Sunday in their first direct presidential election, a watershed event in the country's 91-year history that could cement Prime Minister Recep Tayyip Erdogan's position as Turkey's all-powerful leader.

Erdogan, who has dominated Turkish politics for more than a decade, is the strong front-runner to replace incumbent Abdullah Gul for a five-year term.

"The people are making an important decision ... for Turkish democracy, for the future of our country," Erdogan said after casting his ballot on the Asian side of Istanbul, the country's largest city.

Now in his third term as prime minister at the head of the Islamic-rooted Justice and Development Party, or AKP, Erdogan has been a polarizing figure. He is fervently supported by many as a man of the people who has led Turkey through a period of economic prosperity. Yet critics view him as an increasingly autocratic leader bent on concentrating power and imposing his religious and conservative views on a country founded on strong secular traditions.

Some 53 million people are eligible to vote; an absolute majority is needed to win. Otherwise, the top two candidates go to a runoff on Aug. 24. Erdogan, whose party won local elections in March with about 43 percent of the vote, is widely expected to be elected, although it is unclear if he can avoid a runoff.

Party rules barred Erdogan from serving another term as prime minister. Turkish presidents used to be elected by parliament but Erdogan's government pushed through a constitutional amendment in 2007, changing the procedure to a popular vote.

Previously a largely ceremonial role, Erdogan has vowed to transform the presidency into a powerful position — something his detractors say proves he is bent on a power grab. He has said he will activate the post's rarely used dormant powers — a legacy of a 1980 coup — including the ability to call parliament and summon and preside over Cabinet meetings.

Erdogan's main challenger is Ekmeleddin Ihsanoglu, a 70-year-old academic and former head of the Organization of Islamic Cooperation who is backed by several opposition parties, including the two main ones: a pro-secular party and a nationalist one.

Ihsanoglu, who has focused on a message of unity, said some voting irregularities had been reported Sunday, with some voters photographing their stamped ballots with their mobile phones. The implication is they would use the photos to receive favors from the parties they voted for.

An official complaint would be filed, Ihsanoglu said.

"The eyes of the whole world are upon us," he said after voting in Istanbul. "(Turkey) has been striving to become a first-class democracy ... and hopefully Turkey will achieve this today."

The third presidential candidate is Kurdish politician Selahattin Demirtas, 41, a rising star on the minority Kurdish political scene.

Asa Lindestam, head of a group of election observers from the Organization for Security and Cooperation in Europe, said voting at the few polling stations she had monitored had proceeded "smoothly."

The past year-and-a-half has been a turbulent one for Erdogan, who faced widespread anti-government protests in 2013 triggered by a violent police crackdown on demonstrators objecting to a construction plan in central Istanbul.

More anti-government protests erupted in May after 301 miners died in a coal mine fire blamed on shoddy safety practices. Erdogan and his son have also been implicated in a corruption scandal that he has dismissed as a coup plot by a moderate Islamic preacher and former ally living in the United States, Fethullah Gulen.

Dozens of judicial and police officials involved in the probe against him have been dismissed or re-assigned, and dozens of police have been arrested and jailed.

"The key criteria, or litmus test, will be what percentage of the votes does Prime Minister Erdogan secure in the first round of presidential elections," said Fadi Hakura, an associate fellow at the Chatham House think tank in London.

A percentage below what his party won in local elections could indicate his popularity is waning, Hakura said.

Erdogan's critics say he unfairly dominated the vastly one-sided election campaign, using the resources of his office to monopolize media coverage and crisscross the country. He has denied any inappropriate use of state assets.

Fraser reported from Ankara. Ezgi Akin in Ankara contributed.