"On referendum day there were no major problems, except in some regions, however we can only regret the absence of civil society observers in polling stations", Parliamentary Assembly of the Council of Europe delegation head Cezar Florin Preda said in a statement.
Preda was joined by Tana de Zulueta, head of another team of worldwide observers, who said the referendum fell short of global standards.
At a press conference at the party headquarters in Ankara, Tezcan said the only possible solution to the debates over the referendum's legitimacy were for it to be cancelled by the electoral council.
Turkey's longstanding bid for European Union membership was already in doubt and could be dropped for good if Erdogan follows through on suggestions to reintroduce the death penalty, which he reiterated after the referendum win. The head of the observation mission, Tana de Zulueta, added that unstamped ballot papers that were submitted "contradicted the law".
An unprecedented electoral board decision to accept ballots that didn't bear the official stamp has led to outrage among the opposition.
The European Commission has called on Turkey to seek a national consensus following a referendum result that will substantially increase the powers of the office held by President Recep Tayyip Erdogan.
The main opposition Republican People's Party (CHP) and the pro-Kurdish Peoples' Democratic Party (HDP) said they would challenge the results from most of the ballot boxes due to alleged violations.
The proposed changes would grant the president powers to appoint ministers, senior government officials and half the members of Turkey's highest judicial body, as well as issue decrees and declare states of emergency.
Around 55 million people were eligible to vote in the referendum.
Turkey's three largest cities - Istanbul, Ankara and Izmir - all voted "No", although "Yes" prevailed in Erdogan's Anatolian heartland.
The overall result is a narrow victory for Mr Erdogan - one small enough to be disputed by his opponents.
The U.S. State Department said it had taken note of the European monitors' concerns and looked forward to a final report, urging the Turkish government to protect the rights and freedoms of all citizens, however they voted.
The margin could cement President Recep Tayyip Erdogan's hold on power in Turkey for a decade and is expected to have a huge effect on the country's long-term political future and its worldwide relations.
Opposition parties cried foul on the vote.
"There is only one decision to ease the situation in the context of the law - the Supreme Election Board (YSK) should annul the election", the Dogan news agency quoted Bulent Tezcan as saying after the CHP alleged widespread violations in Sunday's poll.
Most of the changes won't take effect until after the next presidential and parliamentary elections, slated for November 3, 2019.
The result laid bare the deep divide between the urban middle classes who see their future as part of a European mainstream, and the pious rural poor who favour Erdogan's strong hand. "It is very clear".
15 April 2017
15 April 2017
16 April 2017