The opposition's mayoral candidate urged the ruling party to accept defeat.
In the March 31 local elections, the opposition not only prevailed in a tight race in Istanbul, a city of 15 million residents that is Turkey's financial and cultural center, but took control of Ankara, the capital. Erdogan's party, which had held both cities for decades, contested the results, claiming the elections were "tainted."
The ruling Justice and Development Party, or AKP, won the right for a recount of votes that were previously deemed invalid. But on Sunday, Ali Ihsan Yavuz, a deputy chairman, said the party would appeal to the country's top election authority for a total recount of votes in 38 districts in Istanbul, not just of ballots that were canceled.
The party made the move after the opposition candidate's lead narrowed to 16,380 votes after some 80% of the invalidated ballots were reassessed in the partial recount.
The opposition Republican People's Party maintains that it looks increasingly unlikely that the invalidated ballots will swing the result in Istanbul in favor of the ruling party.
Ekrem Imamoglu, the opposition party candidate, urged the AKP to concede.
"I understand that it is not easy to lose (Istanbul) after ruling it for 25 years, but this is what democracy is about," Imamoglu said. "It's not the end of the world."
imamoglu also asked the Supreme Electoral Board to assume its "historic duty" and avoid decisions that would lead to suspicions of "double standards" in favor of Erdogan's party.
Yavuz insisted Sunday that the elections were marred by "organized irregularities."
The electoral authority is expected to rule on the request for a full recount in the coming days before confirming the final results of the elections at the end of the week.