Turkey referendum: Vote expanding Erdogan powers 'valid'17th April 2017
The Yes vote in the referendum that grants sweeping new powers to the president of Turkey is valid, the head of the electoral body says.
Sadi Guven was speaking after the main opposition Republican People's Party (CHP) cited irregularities, including the use of unstamped ballot papers.
President Recep Tayyip Erdogan's push for an executive presidency succeeded with 51.4% voting for it.
Observers said the process had flaws such as campaigning restrictions.
The Organization for Security and Co-operation in Europe (OSCE) said the referendum took place on an "unlevel playing field" as the two sides did not have equal opportunities.
"We observed the misuse of state resources, as well as the obstruction of 'No' campaign events," it said in a statement.
"The campaign rhetoric was tarnished by some senior officials equating 'No' supporters with terrorist sympathisers, and in numerous cases 'No' supporters faced police interventions and violent scuffles at their events."
However, the OSCE said there were no major problems on referendum day, "except in some regions".
The win was met with both celebrations and protests across Turkey.
Deputy Prime Minister Nurettin Canikli said legal changes to introduce the new system could be completed within a year.
New presidential and parliamentary elections are due on 3 November 2019.
Turnout was said to be as high as 85%.
The CHP has demanded a recount of 60% of the votes. Its deputy head said the result should be annulled altogether. The pro-Kurdish Peoples' Democratic Party (HDP) also challenged the vote.
But Mr Guven said the unstamped ballot papers had been produced by the High Electoral Board and were valid.
He said a similar procedure had been used in past elections.
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.
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