The Anatolia news agency announced a victory for President Recep Tayyip Erdogan’s reform by a wafer-thin margin of 51.3 to 48.7.
But even before TV channels had given that result the country’s largest opposition party, the People’s Republican Party (CHP), accused the state-run agency of lying when it said that its figures came from the national electoral authority.
Having earlier claimed that the No had won, the CHP alleged widespread fraud.
Nearly 1.5 million invalid votes had been included in the final count, according to CHP vice-president Erdal Aksunger, speaking at the party’s headquarters.
The party will challenge results from many polling stations in court, CHP deputy director for information technology Can Karatoprak told RFI.
Even Deputy Prime Minister Veysi Kaynak admitted that the final figure was not the definitive majority the ruling Justice and Development Party (AKP) had hoped for.
Anatolia’s results showed a deeply polarised country, with the three largest cities voting against – although by a narrow margin in the cases of Istanbul and Ankara – and much of the Kurdish-majority south-east voting No by two to one.
Erdogan hoped for a ringing endorsement for his plans for a highly centralised presidential system.