Turkey s referendum campaign was conducted on an "unlevel playing field" and the vote count itself was marred by late procedural changes, global observers said on Monday.
The referendum on constitutional amendments in Turkey on Sunday was not in compliance with the standards of the Council of Europe, worldwide observers from OSCE Office for Democratic Institutions and Human Rights (ODIHR) said in a statement. Under the changes, President Erdogan could stay in power through 2029.
The head of the country's electoral board confirmed the win shortly after Mr Erdogan spoke and said the final results would be known in 11-12 days.
During the campaign, Erdogan repeatedly attacked European countries, including Germany and the Netherlands, accusing them of "Nazi-like" tactics for banning his ministers from speaking to rallies of Turkish voters overseas. The main opposition party has demanded the result be nullified, saying the voting was marred by irregularities.
He added, "The change in the constitution which was accepted with the highest turnout in Turkish history will benefit our nation".
Chancellor Angela Merkel and Foreign Minister Sigmar Gabriel also said the Turkish authorities needed to address concerns about the content and procedure of the referendum raised by European legal experts.
Germany said yesterday the close result showed how divided Turkish society was and that Turkish leaders should open talks with opponents. The European Convention on Human Rights, which new EU member states are required to sign up to, calls for a universal abolition of the death penalty except in rare situations during times of war.
Relations with Europe were strained during the referendum campaign when European Union countries including Germany and the Netherlands barred Turkish ministers from holding rallies to support the changes.
The vote has divided Turkey, with supporters claiming the change will bring stability and efficiency to the government, while opponents have said that the move is a risky step toward one-man rule. The French vote for a new president begins next Sunday.
Under the changes, most of which will only come into effect after the next elections due in 2019, the president will appoint the cabinet and an undefined number of vice-presidents, and be able to select and remove senior civil servants without parliamentary approval.
Erdogan said 25 million people had supported the proposal, which will replace Turkey's parliamentary system with an all-powerful presidency.
Erdogan served as prime minister from 2003 until 2014, when rules were changed to hold direct elections for the office of president, previously a ceremonial role elected by parliament.