ISTANBUL (AP) — Turkish politicians were holding final rallies in the last hours of campaigning on Saturday, the eve of pivotal presidential and parliamentary elections that could significantly shape the NATO member's future.

President Recep Tayyip Erdogan, who is facing the toughest challenge ever in his two decades of power, was speaking at neighborhood rallies in Istanbul, Turkey’s biggest city.

His challenger — Kemal Kilicdaroglu of the pro-secular, center-left Republican People’s Party who is the joint candidate of six opposition parties — held his final rally in the capital, Ankara, on Friday under pouring rain.

On Friday, Erdogan dismissed speculation that he wouldn't cede power if he lost by calling the question “very ridiculous.” In an interview with a dozen Turkish broadcasters, Erdogan said he came to power through democracy and would act in line with the democratic process.

“If our nation decides to make such a different decision, we will do exactly what’s required by democracy and there’s nothing else to do,” he said.

Erdogan said Saturday that he views the elections as a “democracy celebration for our country’s future” and aired videos to undermine his opponent as incapable of leading Turkey.

The opposition’s campaign was continued by Istanbul's popular mayor, Ekrem Imamoglu, who held final rallies in the city to call on people to vote for Kilicdaroglu.

On Friday, Kilicdaroglu asked tens of thousands gathered to hear his final speech to go vote on Sunday to “change Turkey’s destiny.” He said he was ready to bring democracy to Turkey, a major criticism of Erdogan who has cracked down on dissent in recent years.

“We will show the whole world that our beautiful country is one that can bring democracy through democratic means,” he said. Though Kilicdaroglu and his party have lost all past elections since he took the helm of the party in 2010, opinion polls have showed he has a slight lead over Erdogan.

Voter turnout in Turkey is traditionally strong, showing continued belief in this type of civic participation in a country where freedom of expression and assembly have been suppressed.

If no presidential candidate secures more than 50% of the vote, a runoff election will be held on May 28.

Turkey’s Supreme Electoral Board said it decided that votes cast for another candidate, Muharrem Ince, who pulled out of the race this week would be counted as valid and that his withdrawal would not be considered until a potential second round.