ISTANBUL (AP) — The Latest on the referendum in Turkey, set to decide whether more power should be concentrated in the hands of the president (all times local):

8:35 p.m.

Officials say Turkish President Recep Tayyip Erdogan is thanking allies and supporters for the passage of a constitutional referendum he backed that greatly expands his powers.

Officials said Erdogan called nationalist allies on Sunday night to congratulate them for the result as vote-counting was continuing, but nearly completed.

With 97 percent of votes counted Sunday, 51.4 percent backed the constitutional changes.

Erdogan supporters were celebrating with fireworks in Istanbul as the vote count was winding up.

Erdogan says he is “grateful” to the people who “reflected their will’

However, the vice-chairman of Turkey’s main opposition party says the party will contest 37 percent of the votes counted.

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8:16 p.m.

Results from Turkey’s state news agency show the “yes” side appearing to be heading toward a narrow victory in the country’s referendum on whether to expand President Recep Tayyip Erdogan’s powers.

The Anadolu agency said that with 97 percent of votes counted Sunday, 51.4 percent backed the constitutional changes to replace Turkey’s parliamentary system with a presidential vote, with 48.6 percent voting against them.

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7:25 p.m.

Turkey’s state news agency says the lead for the “yes” side in the country’s referendum on expanding the president’s powers has narrowed to 4 points with 94 percent counted.

Results carried by Turkey’s state-run Anadolu news agency show the “yes” votes were leading with nearly 52 percent in Sunday’s referendum.

Earlier returns had shown the “yes” votes leading by 10 points, but the gap gradually narrowed as more results came through.

If the “yes” vote prevails in Sunday’s historic referendum, the 18 constitutional changes will replace Turkey’s parliamentary system of government with a presidential one.

The changes include abolishing the office of the prime minister and granting sweeping executive powers to President Recep Tayyip Erdogan.

Opponents fear the changes will lead to autocratic one-man rule by the 63-year-old Erdogan.

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6:55 p.m.

Turkey’s main opposition party has criticized the decision of the country’s elections board to accept as valid ballot papers that don’t have its official stamp.

Republican People’s Party deputy chairman Bulent Tezcan told reporters Sunday that the decision leaves the results of the constitutional referendum “faced with a serious legitimacy problem.”

Turkey’s Supreme Election Board announced the unprecedented move after many voters casting their votes in the country’s historic referendum complained that they were given ballot papers without the official stamp. The board says the ballot papers would be considered as invalid only if proven that they were cast fraudulently.

In previous votes, ballot papers without the official seal were declared to invalid.

Tezcan said: “The Supreme Electoral Board has changed the rules of the vote….This amounts to the SEB allowing fraud in this vote.”

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6:40 p.m.

Turkey’s Supreme Election Board has announced that ballot papers that don’t bear the board’s official seal will be deemed valid and counted.

The board said it made the unprecedented decision Sunday after many voters who cast their votes in the country’s historic presidential referendum complained that they were given ballot papers without the official stamp.

In previous elections, ballot papers without the official seal were declared invalid.

The board says ballot papers for the referendum will be considered invalid only if it’s proven that they were cast fraudulently.

Voters were asked to check that their ballot papers bore the official stamp.

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6:20 p.m.

Turkey’s state-run Anadolu news agency says with 57 percent of ballots counted, the “yes” votes are leading with 56.5 percent in a referendum on whether to expand the president’s powers.

If the “yes” vote prevails in Sunday’s historic referendum, the 18 constitutional changes will replace Turkey’s parliamentary system of government with a presidential one, abolishing the office of the prime minister and granting sweeping executive powers to President Recep Tayyip Erdogan.

Erdogan and his supporters say the “Turkish-style” presidential system would bring stability and prosperity in a country rattled by a coup attempt last year and a series of devastating attacks by the Islamic State group and Kurdish militants.

Opponents fear the changes will lead to autocratic one-man rule by the 63-year-old Erdogan, who has been accused of repressing rights and freedoms.

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6 p.m.

Turkey’s state-run news agency says that “yes” votes are leading in Turkey’s referendum on expanding presidential powers.

The Anadolu Agency says an estimated 38 percent of votes have been tallied and the “yes” side stands at nearly 60 percent of the tally.

If the “yes” vote prevails, the 18 constitutional changes will replace Turkey’s parliamentary system of government with a presidential one, abolishing the office of the prime minister and granting sweeping executive powers to the president.

Critics say the move grants too sweeping executive powers to President Recep Tayyip Erdogan.

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5 p.m.

Polling stations have closed in Turkey’s landmark referendum on whether to approve constitutional amendments greatly expanding presidential powers.

Results are expected later Sunday. Turkey has no official exit polls and media are barred from publishing or broadcasting election results until the High Election Board lifts the ban at 1800 GMT or earlier.

If the “yes” vote prevails, the 18 constitutional changes will replace Turkey’s parliamentary system of government with a presidential one, abolishing the office of the prime minister and granting sweeping executive powers to President Recep Tayyip Erdogan.

Erdogan and his supporters say the “Turkish style” presidential system would bring stability and prosperity in a country rattled by a failed 2016 coup and a series of deadly attacks by the Islamic State group and Kurdish militants.

But opponents fear the changes would lead to autocratic one-man rule, ensuring Erdogan, who has been accused of repressing rights and freedoms, could govern until 2029 with few checks and balances.

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4:50 p.m.

Turkey’s state-run news agency says at least eight people wanted by authorities for their alleged links to outlawed groups have been detained at polling stations.

Anadolu Agency said the suspects were detained in the cities of Adana, Malatya and Trabzon on Sunday by police who were waiting at polling stations for them to cast their votes in Turkey’s historic referendum on whether to expand the president’s powers.

At least five the individuals were detained for alleged links to the Kurdistan Workers’ Party, or PKK, according to Anadolu.

The three others were wanted for ties to a movement led by U.S.-based Muslim cleric Fethullah Gulen, which Turkey accuses of carrying out last summer’s failed military coup.

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4:10 p.m.

Polling stations in Turkey’s 32 eastern provinces have closed for the country’s historic referendum on whether to expand presidential powers.

Voting in the more populous western provinces will end an hour later at 5 p.m. local time (14:00 GMT).

If the “yes” vote wins, 18 constitutional amendments would transform Turkey’s system of government from parliamentary to presidential, abolish the office of the prime minister and grant sweeping executive powers to the president.

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3:50 p.m.

Turkey’s state-run news agency says the death toll in a fight outside a polling station in the southeastern province of Diyarbakir has risen to three.

Anadolu news agency said a land feud may have been the reason for Sunday’s deadly quarrel, while the private Dogan news agency reported it as caused by “differences in political opinion.”

The fight took place outside a village school where voting is going on for Turkey’s historic referendum on expanding the president’s powers.

Anadolu said two people were detained and gendarmes took security precautions at the village.

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3:40 p.m.

The leader of Turkey’s main nationalist party has cast his vote for the referendum in Ankara.

The Nationalist Action Party’s Devlet Bahceli, a supporter of the constitutional amendments proposed in the referendum, described the vote as “an important turning point in the lives of our people.”

The party, the fourth largest in parliament, has backed Turkey’s President Recep Tayyip Erdogan and the ruling Justice and Development Party in their push to change Turkey’s parliamentary system into a presidential one.

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1:30 p.m.

Observers from the 57-nation Organization for Security and Co-operation in Europe are monitoring the voting process in the Turkish capital as the country headed to polling stations in a historic referendum.

Tana de Zulueta, the head of the OSCE observation mission, said the group has been in the country since March 17 “to assess the campaign including the media environment, the legal framework, the conduct of the campaign for its conformity with international standards to which Turkey is party.”

She said observers visited polling stations in 12 locations Sunday to complete its referendum assessment mission.

President Recep Tayyip Erdogan sharply criticized OSCE on Friday, saying, “Who are you? First know your place. You cannot meddle in what happens.”

The group is expected to hold a news conference Monday on their preliminary findings and conclusions regarding the referendum process.

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1 p.m.

Turkey’s state-run news agency says two people have died in a fight outside a polling station in the southeastern province of Diyarbakir.

Anadolu news agency said a quarrel between two families turned deadly Sunday in a village school’s garden where people were casting their votes on Turkey’s referendum.

Voters are deciding Sunday whether to approve or reject changes that greatly expand the president’s powers.

The agency said the reasons for the fight were unknown. The private Dogan news agency reported it as caused by “differences in political opinion.”

One person remains hospitalized, and two others have been detained in the incident.

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12:20 p.m.

Kemal Kilicdaroglu, the leader of Turkey’s main opposition party and campaigner for a “no” vote in the referendum on constitutional amendments, has cast his ballot in the capital Ankara.

“We are voting for Turkey’s fate today,” Kilicdaroglu said, adding: “we hope the results will be good and together we can have the opportunity to discuss Turkey’s other fundamental problems.”

Kilicdaroglu, who leads the Republican People’s Party, has been a vocal critic of the proposed constitutional amendments, arguing that increased presidential powers would lead to “one-man rule” in Turkey.

More than 55 million people are registered to vote in Sunday’s historic referendum.

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12 p.m.

Turkey’s President Recep Tayyip Erdogan has cast his ballot in Istanbul in a referendum he described as a “not an ordinary vote.”

Speaking to reporters after voting, Erdogan said: “We have held referendums before. But this referendum is now about a new administrative system for the Republic of Turkey, it’s a choice for change and transformation.”

“We need to make a decision that is beyond the ordinary,” he said, adding that he hopes the nation will make the “expected” decision.

“I believe in my nation’s democratic common sense,” he said.

Bodyguards with automatic weapons stood guard outside the polling station as the president and his wife Emine Erdogan cast their ballots. Two of their grandchildren accompanied the couple.

Scores gathered to greet the president and snap pictures outside the polling station.

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11 a.m.

Turkey’s Prime Minister Binali Yildirim has cast his vote in the western province of Izmir, saying the outcome of the referendum is for the nation to decide.

Speaking to reporters outside the polling station after casting his vote, he said: “Whatever the result is, we will hold it in high esteem. The decision of our nation is the most beautiful decision.”

The crowd in the polling station chanted, “Turkey is proud of you.”

Both Yildirim and President Recep Tayyip Erdogan have led the campaign for a “yes” vote in the months leading up to the referendum.

Voters are deciding on Sunday whether to approve constitutional amendments that would replace the parliamentary system with a presidential one, scrapping the office of the prime minister and handing its powers to the president.

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10:20 a.m.

Turkish Foreign Minister Mevlut Cavusoglu has lambasted foreign countries for attempting to influence Turkey’s historic referendum as he cast his vote in the southern province of Antalya.

Cavusoglu said some “from abroad” ”tried to tell the Turkish nation what to do. They took sides but today the decision belongs to our nation.”

He did not specify who he was referring to, but tensions have been high between Turkey and some European countries, particularly Germany and the Netherlands. President Recep Tayyip Erdogan branded both countries Nazis for not allowing Turkish ministers to campaign for a “yes” vote there.

The Netherlands withdrew Cavusoglu’s landing permission in March, barring him from addressing expatriate Turks there. Turkey said it would impose sanctions and halted high-level political discussions.

Polls opened Sunday in a crucial referendum on whether to increase presidential powers.

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9:40 a.m.

People were already lined up at an Istanbul polling station before it opened for Turkey’s historic referendum on whether to grant sweeping powers to the president’s office.

“We are here early to say ‘no’ for our country, for our children and grandchildren,” said retired tax officer Murtaza Ali Turgut. His wife Zeynep agreed, saying: “I was going to come sleep here last night to vote at first light.”

Another “no” voter, Husnu Yahsi, said: “I don’t want to get on a bus with no brake system. A one-man system is like that.”

In another Istanbul neighborhood, a “yes” voter expressed full support of President Recep Tayyip Erdogan. “Yes, yes, yes. Our leader is the gift of God to us. We will always support him. He’s governing so well,” Mualla Sengul said.

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7 a.m.

The first polling stations have opened in Turkey’s historic referendum on reforms that would concentrate power in the hands of the nation’s president.

The 18 constitutional changes would convert Turkey’s system of government from parliamentary to presidential, and abolish the office of the prime minister.

President Recep Tayyip Erdogan, who called the referendum and has championed the “yes” campaign, says the proposed “Turkish style” presidential system will ensure the country no longer risks having weak governments. Opponents fear the change will lead to autocratic one-man rule, ensuring Erdogan, who has been accused of repressing rights and freedoms, could govern until 2029 with few checks and balances.

Polls in the east opened at 7 a.m. (0400 GMT), while those in the west are to open an hour later.