Turkish President Recep Tayyip Erdogan sought to project confidence Sunday in a close election that could end his two-decade hold on power in the predominantly Muslim country that comprises NATO’s second-largest military force.

“My hope to God is that after the counting concludes this evening, the outcome is good for the future of our country, for Turkish democracy,” Mr. Erdogan told supporters after casting his vote in Istanbul.

There was no definitive result as polls closed Sunday evening across Turkey, where the 69-year-old president faces his thorniest challenge in years amid domestic economic turmoil, eroding democratic norms and criticism of his government’s response to a massive earthquake in February.

Analysts said Mr. Erdogan might be unseated by leading opposition candidate Kemal Kilcdaroglu, who has run on a promise to return Turkey to a more democratic path following years of autocratic moves by the president’s ruling Justice and Development Party, or AKP.

Pre-election polls gave a slight lead to Mr. Kilicdaroglu, 74, the joint candidate of a six-party opposition alliance and the leader of the center-left, pro-secular Republican People’s Party, or CHP.

Crowds mobbed polling stations where Mr. Erdogan and Mr. Kilicdaroglu cast their ballots Sunday, with the opposition leader’s supporters chanting “President Kilicdaroglu!”

“We have all missed democracy so much. We all missed being together,” Mr. Kilicdaroglu said after voting. “From now on, you will see that spring will come to this country.”

His comments reflected years of criticism of Mr. Erdogan. Critics have long said the president has consolidated power in an authoritarian fashion over the past decade, cracked down on media freedom and embraced a brand of Islamist nationalism that has threatened secular democracy in Turkey.

More than 64 million people were eligible to vote in Sunday’s elections. If no candidate receives more than 50% of the vote, the presidential race will be determined in a May 28 run-off.

Voters also cast ballots for lawmakers to fill Turkey’s 600-seat parliament, which has lost significant leverage in recent years amid moves by Mr. Erdogan and the AKP to strengthen the reach and power of the presidency.

If his political alliance wins, Mr. Erdogan could continue governing with minimal restriction on the power he has amassed in Turkey, which he has ruled as either prime minister or president since 2003.

• This article is based in part on wire service reports.

• Guy Taylor can be reached at gtaylor@washingtontimes.com.