Turkey's main opposition party has filed an appeal  at the country's highest administrative court against the result of the recent referendum that expanded President Tayyip Erdogan’s powers.

In the Sunday’s referendum, the “Yes” campaign won over 51 percent of the vote, while the “No” campaign gained nearly 49 percent.

The Republican People's Party's (CHP) lawyer Atilla Kart formally submitted the petition with the Council of State on Friday afternoon over the last-minute decision by the High Electoral Board (YSK) to accept unstamped ballots as valid.

The news comes after Turkey’s highest electoral authority, the YSK, on Wednesday rejected an appeal, which had been made by the main opposition parties over allegations of vote-rigging.

Kart told reporters that the move was not "just for the 'No' voters" but for the protection of all voters' legal rights.

The lawyer added that there were also 'No' voters among the unstamped ballot envelopes that the YSK accepted, describing the situation as "complete lawlessness."

Earlier, CHP's deputy leader, Bulent Tezcan, said the party would file a case urging the annulment of the YSK's decision to allow the rule change.

He had earlier called for the outcome of the referendum not to be finalized until the case was concluded. The results are expected to be confirmed on April 27 or 28.

"Whether citizens said 'Yes' or 'No', we will continue our legal fight until the end to protect the rights of the 49 million citizens who voted," Tezcan said.

Turkish Prime Minister Binali Yildirim slammed the moves as "futile" and said there was "no point in wasting more of everyone's time."

Yildirim told reporters in Ankara that it was "not the democratic way to go to court, to make complaints to fix the people's decision."

He added that the CHP and others had the right to challenge but "there was nothing we could say about using this."

"The people have made their decision.... Disagreeing with the people's decision suggests not believing in democracy as much as necessary," Yildirim added.

Kart noted that the CHP was assessing whether one of the ways to challenge the vote included taking the appeal against the referendum result to the Constitutional Court or the European Court of Human Rights (ECHR).

"Right now, an application can be made to the Constitutional Court or ECHR," he said.

On Thursday, Turkey’s Justice Minister Bekir Bozdag said the ECHR has no jurisdiction to rule on appeals against the result of the recent referendum in the country.

He also said, “If the opposition takes the appeal to the Constitutional Court, the court has no other option than to reject it.”