The board agreed to reject the petitions submitted by the Republican People's Party (CHP), the Peoples' Democratic Party (HDP) and the Patriotic Party to annul the April 16 constitutional reform referendum, the YSK announced in a written statement.
The three parties objected to the decision, and deemed ballot papers without official seals invalid.
"The CHP will use all its democratic rights to ensure the referendum would rerun," party spokesperson Selin Sayek Boke said on Wednesday, private channel NTV reported.
She vowed that her party will "not recognise" the referendum result, arguing that the referendum process was fraudulent and the results were manipulated.
Bulent Tezcan, the CHP Deputy Chairman, said during a televised interview that there is a crisis of legitimacy of the referendum.
According to unofficial results of the April 16 constitutional referendum, the "Yes" campaign won with 51.41 per cent, while the "No" votes stood at 48.59 per cent.
However, the CHP challenged the result. Its leader Kemal Kilicdaroglu slammed on Tuesday YSK's decision to count unsealed ballots in the referendum.
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