Days after Turkey's election authority rejected its request to annul the referendum on boosting the president's powers, the country's main opposition says it will apply to Turkey's highest administrative court.

The opposition party is contesting the results of Sunday's referendum due to a number of voting irregularities, in particular an electoral board decision to accept ballots without official stamps, which breaks Turkish law. International monitors have also noted irregularities in the voting that resulted in a narrow win for President Recep Tayyip Erdogan's "yes" camp.

Deputy chairman Bulent Tezcan said Friday that his Republican People's Party, or CHP, would seek a cancellation of the electoral board's controversial decision at the Council of State. It would also request that the election board not declare official results until the court's ruling.