A member of the Council of Europe’s election observer mission in Turkey said on April 18 that as many as 2.5 million votes may have been tampered with in a closely contested referendum that expanded presidential powers and could allow President Recep Tayyip Erdogan to stay in power until 2029.
Alev Korun, an Austrian member of parliament and part of the observer mission for the Parliamentary Assembly of the Council of Europe (PACE), said the possible manipulation of votes was almost double the margin of Erdogan's victory in the April 16 referendum.
Korun also said questions have arisen about the actual voting.
“This is about the fact that actually the law only allows official voting envelopes. The highest election authority decided however -- as it were, against the law -- that envelopes without official stamp should be admitted," she told ORF radio.
"There is a suspicion that up to 2.5 million votes could have been manipulated," Korun added.
The Organization for Security and Cooperation in Europe (OSCE), which conducted a separate observer mission, said Ankara was not cooperating in an investigation into allegations of voting fraud.
Turkey's main opposition party has formally appealed for the annulment of a referendum to expand Erdogan’s powers, defying the prime minister's call for political forces to respect the official results of the disputed vote.
People's Republican Party (CHP) deputy chairman Bulent Tezcan announced he had filed a request with the High Electoral Board (YSK) on April 18, saying the results of the referendum on constitutional changes are "illegitimate" due to voting irregularities.
The challenge from the secularist party comes amid concerns raised by opposition parties and international voting monitors about major voting irregularities in the April 16 referendum.
Proposed changes that will give the president more power and could enable Erdogan to stay in office until 2029 passed with 51.4 percent of the vote, according to electoral officials.
Erdogan's critics say the reforms will hand extensive power to a man with an increasingly autocratic bent and leave few democratic checks and balances in place.
In an address to legislators from Erdogan's ruling Justice and Development Party (AKP) earlier on April 18, Prime Minister Binali Yildirim said that “the people's will has been reflected at the ballot box, and the debate is over."
"Everyone should respect the outcome, especially the main opposition," he added.
Meanwhile, the European Union urged the country to initiate "transparent investigations" into the allegations of voting irregularities and make efforts to unify the divided nation.
"We call on the Turkish authorities to consider the next steps very carefully, and to seek the broadest possible national consensus in the follow-up to the national referendum," European Commission spokesman Margaritis Schinas said.
Protests In Turkish Cities
Thousands of people took to the streets of Istanbul and other Turkish cities late on April 17 to protest the results of the referendum.
The protesters expressed anger about last-minute changes to the referendum voting procedures and an electoral board decision to allow as valid more than a million ballots cast without an official stamp.
The decision by the YSK to allow unstamped ballots was clearly against the law, prevented proper records being kept, and may have impacted the results, according to the Union of Turkish Bar Associations (TBB).
The bar association expects Turkey's electoral body to realize its constitutional responsibilities in evaluating complaints, a statement said.
Observers from the OSCE and PACE said the legal framework for the referendum “remained inadequate for the holding of a genuinely democratic referendum."
WATCH: Monitors Say Turkish Vote Fell Short Of International Standards
The monitors also said the referendum campaign was conducted on an “unlevel playing field” and that the counting of ballots in the referendum had been marred by "late procedural changes."
U.S. President Donald Trump called Erdogan on April 17 "to congratulate him on his recent referendum victory" and discuss the situation in neighboring Syria.
The U.S. State Department, meanwhile, noted the observers' concerns and urged Turkey to respect diverse viewpoints and "maintain a meaningful political dialogue" with opposition parties.
"We look to the government of Turkey to protect the fundamental rights and freedoms of all its citizens, regardless" of how they voted, it said. "The United States remains committed to strengthening our bilateral relationship [and] continues to support Turkey's democratic development, to which commitment to the rule of law and a diverse and free media remain essential."
Erdogan rejected criticism, saying Turkey does not "see, hear, or acknowledge the politically motivated reports" of the monitors.
Addressing supporters in Ankara, Erdogan said the country could hold a referendum on its long-stalled EU membership bid.
He added that he would approve reinstating the death penalty if it was supported in a referendum or a bill was submitted through parliament, a move that would end Turkey's EU negotiations.
In a separate development, Turkey's council of ministers moved to extend for another three months a state of emergency declared in the wake of a failed July 2016 coup. The extension first must go to parliament for approval.
With reporting by AP and Reuters