As many as 2.5 million votes could have been manipulated in the Turkey referendum which saw a narrow “yes” vote to grant expanded presidential powers, according to observers.
The Council of Europe, which monitored the referendum, had already claimed it was an uneven contest as the “yes” side had dominated campaign coverage, with the arrest of journalists and the closure of media outlets silencing other views.
Alev Korun, a member of the group, said monitors had been prevented from entering voting locations in the majority Kurdish town of Diyarbakir and also raised concerns over videos on social media which appeared to show people voting more than once.
He also said a last-minute decision by the Turkish election authority to allow ballot envelopes without the official stamp was illegal.
“This is about the fact that actually the law only allows official voting envelopes,” Mr Korun said.
“The highest election authority decided however – as it were, against the law – that envelopes without official stamp should be admitted.
“There is a suspicion that up to 2.5 million votes could have been manipulated.
“These complaints are to be taken very seriously and they are, in any case, of such an extent that they would turn around the outcome of the vote.”
The pro-Kurdish opposition Peoples’ Democratic Party has said it presented complaints about unstamped ballots affecting three million voters.
The opposition CHP party will present an appeal for the annulment of the referendum to the High Electoral Board (YSK) on Tuesday.
On Monday, the Union of Turkish Bar Associations (TBB) reiterated that allowing unstamped ballots was against the law.
In a statement, it said: “With this illegal decision, ballot box councils were misled into believing that the use of unstamped ballots was appropriate.
“The YSK announcement, which is clearly against the law, has led to irregularities, and the prevention of records that could uncover irregularities from being kept.”
Turkish President Recep Tayyip Erdogan has dismissed criticism of the referendum.
He refuted concerns raised by international monitors from the Organisation for Security and Co-operation in Europe (OSCE), telling them to “know your place”.
Meanwhile, Turkish Prime Minister Binali Yildirim has said rumours of voting irregularities were a vain effort to cast doubt on the result.
He told parliamentarians: “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.”
A British Foreign Office spokesman said: “We are concerned by the preliminary findings of the OSCE – which included UK observers. We encourage the Turkish authorities to work with the OSCE to address their concerns.
“It is important that Turkey enacts these constitutional changes in a way that sustains democracy, respects the rule of law and protects fundamental freedoms in line with its international commitments.
“As a friend and ally, the UK stands ready to support Turkey in this process.”