ANKARA -- Turkish President Recep Tayyip Erdogan congratulated late on Sunday Ekrem Imamoglu, the opposition's candidate, for winning the Istanbul mayorship.

"I congratulate Ekrem Imamoglu, who has won the election, according to unofficial results," Erdogan tweeted.

According to unofficial results, Imamoglu from Republican People's Party gained 54.03 percent of the votes, while his rival Binali Yildirim from the ruling Justice and Development Party (AKP) had 45.09 percent, as 99.37 percent of the ballots were counted.

Yildirim, the former prime minister, conceded defeat hours earlier and congratulated his opponent in Istanbul's repeated mayoral election.

Imamoglu, who was the mayor of Istanbul's Beylikduzu district for five years, beat Yildirim by a margin of some 13,000 votes in the first election on March 31, when the country held local elections, but the result was annulled by the Supreme Election Board over AKP's claims of irregularities.