The main opposition CHP responded to the electoral board's decision by saying it would employ all legal ways to appeal the referendum.
Turkey's Supreme Electoral Board (YSK) on Wednesday announced that it had rejected appeals from the main opposition parties to annul the referendum that will change Turkey's system of governance from a parliamentary to a presidential system.
The main opposition party, the CHP, had called on the electoral board to repeal Sunday's vote, which was won by the "Yes" camp, because unstamped ballot papers were included in the vote count at the eleventh hour.
"CHP, HDP and Vatan Party appeals regarding the April 16 referendum were discussed separately, and as a result of evaluations, the appeals were rejected with 10 votes against and 1 vote in favour," the electoral board said.
The CHP responded by saying it would employ all legal ways to appeal the referendum.
"This is a serious legitimacy crisis. We will employ all legal ways available. We will evaluate tomorrow whether we will take the decision to the Constitutional Court or the European Court of Human Rights," CHP deputy chairman Bulent Tezcan said.
Turkey's Justice Minister Bekir Bozdag, addressing Tezcan's comments on Thursday, said that the European Court of Human Rights had no jurisdiction to rule on appeals over the referendum in Turkey.
Bozdag also commented on the YSK decision, saying the "Supreme Electoral Board's decision is the right one. The board has evaluated and ruled on similar cases in the past, and this is no different."
The justice minister added that the CHP had previously appealed to the YSK to accept unstamped ballots as valid in the 2015 elections and thus should respect the board's decision.