Turkish President Recep Tayyip Erdogan has declared victory in a referendum

President Tayyip Erdogan declared victory in a referendum on Sunday that will make him far more powerful in the biggest overhaul of modern Turkish politics, but opponents said the vote was marred by irregularities and they would challenge its result.

The “Yes” camp in Turkey’s referendum, led by Yildirim’s boss, President Recep Tayyip Erdogan, appeared to win a slender victory over the “No” vote, getting about 51 percent of the vote.

Turkey’s mainly Kurdish southeast and its three main cities, including the capital Ankara and the largest city Istanbul, looked set to vote “No” after a bitter and divisive campaign.

Erdogan said 25 million people had supported the proposal, which will replace Turkey’s parliamentary system with an all-powerful presidency and abolish the office of prime minister

“There is no loser in this referendum, but only one winner: Turkey and its noble Turkish people,” said Turkish Prime Minister Binali Yildirim.

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%.

But opponents questioned the validity of the vote, calling for a recount and challenging a last minute decision by the electoral authorities to allow ballots to be counted that were not stamped by election officials.

Deputy Prime Minister Mehmet Simsek said there would be no early elections following the result.

The main opposition CHP, the pro-Kurdish People’s Democracy Party and other critics argue that the amendments give too much power to one individual, undermining the separation of powers in the government.

Erdogan survived a failed coup attempt last July, responding with a crackdown that has seen 47,000 people detained and 120,000 sacked or suspended from their jobs.