Turkish opposition lawmaker for the Republican People's Party (CHP), Musa Cam, has submitted an appeal to the European Court of Human Rights, demanding the annulment of the constitutional change referendum that took place on April 16.
Cam said he submitted an individual appeal independently from the one his party is expected to make to the European Court.
In his application, Cam said a decision by Turkey's High Electoral Board (YSK) to allow unstamped ballots in the referendum had caused the outcome to be "illegitimate and not representative of the people's will".
The YSK released the final referendum results on Thursday, showing 51.4 percent support for the "Yes" vote.
They were released despite calls by the CHP to delay a final announcement while they appealed the vote.
The YSK and a Turkish court, the Council of State, have rejected or declined to hear the CHP appeals.
Turkish President Recep Tayyip Erdogan and the "Yes" camp have said appeals by the opposition were an attempt to undermine the results of the vote, adding only the YSK had jurisdiction on the matter.
The constitutional changes approved in the referendum will see Turkey move to a presidential system of governance from a parliamentary one. Under the new system, the president has the authority to draft the budget, declare a state of emergency and issue decrees overseeing ministries.