ISTANBUL — Turkey’s biggest city remained on tenterhooks on Thursday as a recount of votes in a contentious mayoral election entered its third day, with the opposition candidate arguing that his winning margin remained too wide for the ruling party's candidate to overcome.

Ekrem Imamoglu, a former district mayor who ran as a unity candidate on the Republican People’s Party (CHP) ticket, is ahead by 0.2% of the vote in Istanbul, where more than 8.5 million votes were cast, according to preliminary results, putting him on the cusp of a huge upset against the Justice and Development Party (AKP), which has controlled the municipality for 25 years.

His opponent, former Prime Minister Binali Yildirim, has said it is far too early for Imamoglu to declare himself mayor and that both sides must wait for a recount to finish.

So far, the recount of votes that were initially invalidated has been completed in 11 of the 21 Istanbul districts for which the High Election Board initially ordered partial or complete recounts. Imamoglu said the new tally had narrowed his lead slightly to 19,552 votes.