Turkey’s main opposition party has said it will challenge the country’s referendum result after the president won a vote to expand his powers.
The Republican People’s Party (CHP) has questioned the legitimacy of the close result, citing irregularities in the electoral process.
President Recep Tayyip Erdogan’s push for an executive presidency succeeded with just over 51% of the vote.
The win was met with both celebrations and protests across Turkey.
The CHP is refusing to accept the “Yes” victory and is demanding a recount of 60% of the votes, criticizing a decision to pass unstamped ballot papers as valid unless proven otherwise.
Three of Turkey’s biggest cities – Istanbul, Ankara and Izmir – all voted “no” to the constitutional changes.
Opposition supporters took to the streets of Istanbul to bang pots and pans – a traditional form of protest – in a series of noisy demonstrations.
Meanwhile, flag-waving supporters of Mr Erdogan celebrated as their president praised them for their “historic decision” that could keep him in office until 2029.
With 99.97% of ballots counted, the “Yes” campaign had won 51.41% of the votes cast, while “No” had taken 48.59%. Turnout was said to be as high as 85%.
Separately, three people were shot dead near a polling station in the south-eastern province of Diyarbakir, reportedly during a dispute over how they were voting.
Responding to Sunday’s result, the European Commission issued a statement urging Mr. Erdogan to respect the closeness of the vote and to “seek the broadest possible national consensus” when considering the far-reaching implications of the constitutional amendments.
“Today… Turkey has taken a historic decision,” Mr Erdogan told reporters at his official Istanbul residence, the Huber Palace. “With the people, we have realized the most important reform in our history.”
He called on everyone to respect the outcome of the vote.
The president also said the country could hold a referendum on bringing back the death penalty – a move that would end Turkey’s EU negotiations.
Deputy Prime Minister Veysi Kaynak admitted the “Yes” vote had been lower than expected.