ISTANBUL — President Recep Tayyip Erdogan of Turkey claimed victory by a narrow and still-contested margin in a referendum that grants sweeping powers to his office, in a watershed moment that the country’s opposition fears may cement his one-man rule.
With just under 99 percent of ballots counted, “Yes” had 51.33 percent of votes cast, and “No” had 48.67 percent, according to the state-run news agency, Anadolu.
But the country’s election commission has yet to announce official results, and Turkey’s main opposition party said they would demand a recount of about 37 percent of ballot boxes, containing around 2.5 million votes.
The constitutional change, if it stands, will allow the winner of the 2019 presidential election to assume full control of the government, ending the current parliamentary political system.
Its ramifications, however, would be immediate. The “yes” vote in the referendum would be a validation of the current leadership style of President Erdogan, who has been acting as a de facto head of government since his election in 2014 despite having no constitutional right to wield such power as the office of the president was meant to be an impartial role that lacks full executive authority.
The result would tighten Mr. Erdogan’s grip on the country, which is one of the leading external actors in the Syrian civil war, a major way station along the migration routes to Europe and a crucial Middle Eastern partner of the United States and Russia.
The referendum was conducted in an atmosphere of fear, with the campaign characterized by prolonged intimidation of opposition members, several of whom were shot at or beaten while on the stump by persons unknown.
The opposition questioned the legitimacy of the referendum after the election board made a last-minute decision to increase the burden needed to prove allegations of ballot-box stuffing. At least one instance of alleged voter fraud appeared to be captured on camera.
“We are receiving thousands of complaints on election fraud; we are evaluating them one by one,” said Erdal Aksunger, the deputy head of the Republican People’s Party, or C.H.P.
Since a failed coup last summer, Turkey has been under a state of emergency, a situation that allowed the government to fire about 130,000 people suspected of being connected to the failed putsch, and to arrest about 45,000.
The new system will, among other changes:
• Abolish the post of prime minister and transfer executive power to the president.
• Allow the newly empowered president to issue decrees and appoint many of the judges and officials responsible for scrutinizing his decisions.
• Limit the president to two five-year terms, but give the option of running for a third term if Parliament truncates the second one by calling for early elections.
• Allow the president to order disciplinary inquiries into any of Turkey’s 3.5 million civil servants, according to an analysis by the head of the Turkish Bar Association.
Members of the opposition are concerned that the new system will threaten the separation of powers on which liberal democracies have traditionally depended.
“It represents a remarkable aggrandizement of Erdogan’s personal power and quite possibly a death blow to vital checks and balances in the country,” said Professor Howard Eissenstat, a Turkey expert at the Project on Middle East Democracy, a Washington think tank. “Judicial independence was already shockingly weak before the referendum; the new system makes that worse.”
Mr. Erdogan’s supporters say the new system will not limit political and judicial oversight. If opposition parties win control of Parliament, they could override the president’s decrees with their own legislation, while also asserting greater control over judicial appointments, supporters of the new Constitution contend.
The victorious “yes” camp also argues that a strong, centralized government will make Turkey better able to tackle its many challenges, including a troubled economy, the world’s largest Syrian refugee population, two terrorism campaigns, a civil war against Kurdish insurgents and the Syrian war across Turkey’s southern border.
“Stable governments have been able to handle crises more effectively, implement structural reforms in due time and render the investment climate more favorable by increasing predictability,” Mr. Erdogan’s spokesman, Ibrahim Kalin, wrote in a commentary piece for CNN’s website.
The fearful environment in which the referendum was conducted has led watchdogs to question the fairness of the campaign. In addition to the vast purges of perceived opposition members, the authorities also often prevented “no” campaigners from holding rallies and events. And Mr. Erdogan and his allies frequently implied that their opponents were allied with terrorist groups or the suspected leaders of last year’s failed coup.
Analyses of television coverage showed that the “yes” campaign received disproportionately more airtime than its opponents.
Hundreds of election observers were also barred from monitoring the vote, and thousands of Kurds displaced by fighting in southeastern Turkey may not have been able to vote because they have no address, according to the Independent Election Monitoring Network, a Turkish watchdog.
“The current political climate and the atmosphere of fear makes the timing of the referendum a worrisome one,” the network said in a report published on the eve of the poll.
Now that Mr. Erdogan has won the referendum, analysts are divided about what he will do next.
Some believe he may initially try to rebuild his relations with the West, which were severely damaged during the referendum campaign as he sought to manufacture diplomatic crises in order to energize his base at home.
After Germany and the Netherlands blocked Turkish officials from campaigning in those countries, Mr. Erdogan said that both nations had demonstrated Nazi-like behavior, drawing a rebuke from leaders like Chancellor Angela Merkel of Germany.
Ozgur Unluhisarcikli, the director of the Ankara office of the German Marshall Fund of the United States, a think tank, said he expected a victorious Mr. Erdogan to lead “a charm offensive towards Europe and the U.S. to gain validation of the new system — and such a charm offensive might include correcting some of the democratic backsliding that we’ve seen in Turkey.”
“On the other hand, if his charm offensive is not reciprocated,” Mr. Unluhisarcikli added, “then he might start initiating a Plan B, which involves tightening his grip on Turkish society.”
But Professor Eissenstat said it was unlikely that Mr. Erdogan would spend any time repairing relationships with the opposition.
“Some people have imagined that Erdogan might reboot after a ‘yes’ victory and reach out to the opposition,” he said. “I don’t think that is likely. The purges will continue; Erdogan’s instinct is to crush opposition, not co-opt it.
“The question is whether further centralization of power and increased repression can bring stability and allow Erdogan to reboot a troubled economy,” Professor Eissenstat added. “The record of the past 10 years is that the opposite is true.”