Nationalist Movement Party (MHP) leader Devlet Bahçeli said late Sunday that the referendum results were "a very important success" as Turkey leaned 'Yes' in the polls.

Bahçeli called the outcome "an undeniably successful achievement; a win that makes neglect and denial impossible."

He said Turkey rejected international "pressure, blackmail, imposition, force and threats by the whole world to put the 'no' choice forward."

Unofficial results showed that the "Yes" vote prevailed in Turkey's historic constitutional reform referendum on switching to a presidential system with more than 97 percent of ballot boxes opened.

As of 8:05 p.m., 'Yes' votes were at 51.39 percent, while the 'No' vote stood at 48.61 percent.

The data showed that Turkey's three biggest cities - Istanbul, Ankara and Izmir - as well as the predominantly Kurdish southeast voted "No", however, the "Yes" campaign still performed better than expected in the southeast where the region heavily voted for pro-PKK HDP in the general elections in 2015.

With more than 90 percent of the votes counted, preliminary results showed that a great majority of MHP voters sided with the "No" side in the referendum. Bahçeli had openly backed the 'Yes' side and President Recep Tayyip Erdoğan throughout the referendum campaign.

Although the votes of the MHP and the ruling Justice and Development Party (AK Party) votes were 61.39 percent in the Nov. 1, 2015 referendum, "Yes" votes barely exceeded 51 percent in this year's referendum. AK Party votes were 49.49 percent in Nov. 1 elections.