ANKARA, Turkey — Turkey held high-stakes presidential and parliamentary elections on Sunday that could consolidate President Recep Tayyip Erdogan’s grip on power or curtail his vast political ambitions. Opposition leaders cast their ballots vowing to be vigilant against voting fraud.

The elections will complete Turkey’s transition to a new executive presidential system, a move approved in a controversial referendum last year.

Erdogan, 64, is seeking re-election for a new five-year term with hugely increased powers under the new system, which he insists will bring prosperity and stability to Turkey, especially after a failed coup attempt in 2016 that has left the country under a state of emergency since then. His ruling Justice and Development Party, or AKP, is hoping to retain its majority in parliament.

Still, Erdogan — who has been in power since 2003 — is facing a more robust, united opposition this time. Opposition candidates have vowed to return Turkey to a parliamentary democracy with strong checks and balances and have decried what they calls Erdogan’s “one-man rule.”

Five candidates are running against Erdogan in the presidential race. Although Erdogan is seen as the front-runner, he must secure more than 50 percent of the vote Sunday for an outright win. If that threshold is not reached, a runoff could be held on July 8 between the leading two contenders.

Erdogan’s main challenger is 54-year-old former physics teacher Muharrem Ince, who is backed by the center-left main opposition Republican People’s Party, or CHP. Ince has wooed crowds with an unexpectedly engaging election campaign and his rallies in Turkey’s three main cities of Istanbul, Ankara and Izmir drew massive numbers.

Also challenging Erdogan is 61-year-old former Interior Minister Meral Aksener. The only female presidential candidate, she broke away from Turkey’s main nationalist party over its support for Erdogan and formed the center-right, nationalist Good Party.

More than 59 million Turkish citizens — including 3 million expatriates — are eligible to vote in Sunday’s elections. Erdogan called the ballots more than a year earlier than scheduled in what analysts say was a pre-emptive move ahead of a possible economic downturn.

Both Ince and Aksener vowed to watch out for voting fraud on Sunday.

“I hope these elections are beneficial and truly reflect the free will of the voters,” Aksener told reporters in Istanbul.

Ince, who cast his vote in his hometown of Yalova, in northwest Turkey, said he was returning to Ankara where he would monitor the vote count at the High Electoral Board against what he fears could be irregularities.

Selahattin Demirtas, the candidate of the pro-Kurdish Peoples’ Democratic Party, or HDP, was forced to run his campaign from prison, where he is being held in pre-trial detention on terrorism-related charges. Demirtas denies any wrongdoing, saying that his imprisonment is politically motivated so that Erdogan’s government can stay in power.

Voting on Istanbul’s Asian side, 59-year-old Sebnem Izgit said: “Our hope is Muharrem Ince. I hope that we will wake up to a more beautiful day tomorrow.”

“We are voting for a better country for our children,” driver Cem Gursen said.

Turkey will also be electing 600 lawmakers to parliament on Sunday — 50 more than in the previous assembly. The constitutional changes have allowed parties to form alliances, paving the way for Ince and Aksener’s parties to join a small Islamist party in the “Nation Alliance” against Erdogan.

The pro-Kurdish HDP was left out of the alliance and needs to pass a 10 percent threshold to win seats in parliament. If it does that it could cost Erdogan’s AKP and its nationalist ally in the “People Alliance” dozens of seats — leading it to lose its parliamentary majority.

The campaign coverage has been lopsided in favor of Erdogan who directly or indirectly controls a majority of Turkey’s media. The elections are also being held amid fears of possible irregularities. The Organization for Security and Cooperation in Europe is monitoring the elections with as many as 350 observers.

Recent changes to electoral laws allow civil servants — people on the government payroll — to lead ballot box committees and security forces can be called to polling stations.

Citing security reasons, authorities have relocated thousands of polling stations in predominantly Kurdish provinces, forcing some 144,000 voters to travel further to cast their ballots. Some will even have to pass through security checkpoints to vote.

Ballot papers that don’t bear the official stamps will still be considered valid — a measure that led to allegations of fraud in last year’s referendum.

The vote is taking place under a state of emergency declared after the failed coup attempt, which allows the government to curtail civil rights. Some 50,000 people have been arrested and 110,000 civil servants have been fired under the emergency powers, which opposition lawmakers say Erdogan’s government is using to stifle dissent.

The pro-Kurdish HDP, which has seen nine of its lawmakers and thousands of party members arrested by the government, also says more than 350 of its election workers have been detained since April 28.

AP