By Tuvan Gumrukcu, Ece Toksabay and Tulay Karadeniz

ANKARA (Reuters) – Turkey’s ruling AK Party set out plans on Wednesday for President Tayyip Erdogan to gradually take back the party reins, in a sign it would begin implementing changes approved in Sunday’s referendum despite opposition attempts to annul it.

Prime Minister and AKP leader Binali Yildirim said Erdogan can rejoin the party he founded in 2001 once official results of the plebiscite, granting him sweeping powers, are announced. Those results are expected before the end of the month.

But he said the AKP would not hold a party congress until 2018, indicating Erdogan would not officially become its leader until then. There were widespread expectations he would take over the leadership almost immediately after the vote.

“When the High Electoral Board (YSK) announces official results, our president will be able to return to the party,” Yildirim told reporters in front of AKP headquarters.

His comments came as the YSK met to evaluate appeals to annul the referendum and after the bar association and an international monitor said the board had acted illegally by allowing unstamped ballot papers to be counted, and may have swung the vote.

A defiant Erdogan, whose narrow victory exposed the nation’s deep divisions, has said Sunday’s vote ended all debate on the more powerful presidency he has long sought, and Turkey would ignore criticism of the referendum from European observers.

The pro-Kurdish opposition HDP filed an appeal on Wednesday for an annulment on the grounds there had been widespread violations, a day after a similar move by the main opposition CHP. [I7N1G2024]

HDP deputy chairman Mithat Sancar said the vote was undermined by the fact that the campaign was held under emergency rule while the party’s co-leaders were under arrest, that its candidates for polling station monitors were rejected, and that state resources were used in the “yes” campaign.

He said the electoral board’s last-minute decision to allow unstamped ballots had prevented proper record-keeping, meaning that it was now impossible to determine how many invalid or fake votes may have been counted. Some voters had been unable to cast their ballots in private, he added.

“This referendum will forever remain controversial,” he told reporters. “You cannot build a change in the political system on such a controversial and unfair referendum.”

Foreign Minister Mevlut Cavusoglu said on Wednesday a critical report by European observers on the referendum contained several mistakes which he believed were deliberate.

Observers from the Organisation for Security and Cooperation in Europe (OSCE) and the Council of Europe said Sunday’s referendum had been an uneven contest.

“The OSCE’s report has no reliability as their observations lack objectivity and are extremely partial,” Cavusoglu told a news conference in Ankara.

(Writing by Daren Butler; Editing by David Dolan and Mark Trevelyan)