Initial results showed the main opposition Republican People's Party (CHP) narrowly won control of Turkey's largest city, thereby ending 25 years of control of a key power center by the AKP and its Islamist predecessors.
The loss of Istanbul, Turkey's financial hub, would be a blow to Erdogan, who campaigned hard ahead of the vote. The post-vote uncertainty has kept financial markets on edge and contributed to a nearly 5 percent slide in the lira.
In the 16 days since the election, the AKP has filed numerous appeals for vote recounts across Istanbul, a city of more than 15 million people. The High Election Board (YSK) has approved some of those objections, ordering partial or full recounts in several districts.
AKP Deputy Chairman Ali Ihsan Yavuz submitted his party's extraordinary appeal for the annulment and renewal of the vote to the YSK on Tuesday, saying thousands of votes were impacted by the irregularities.
"There is clearly an organized unlawfulness, an election fraud here. The only authority that can end this controversy is the YSK," Yavuz told reporters in Ankara.
SUITCASES OF DOCUMENTS
He said 16,884 votes were marked as either invalid or added to the tallies of other parties in the elections. He said the AKP had submitted three suitcases of documents to the YSK to prove the irregularities.
If the appeal is approved, a second election would take place on June 2. If rejected, the results would be finalized and the CHP's Ekrem Imamoglu would receive his mandate as mayor.
Yavuz said the gap between Imamoglu and his AKP rival, former Turkish prime minister Binali Yildirim, had fallen to 13,900 votes from around 28,000 as a result of the recounts.
If all votes had been recounted across the city the AKP would have won, Yavuz added.
The repeated AKP challenges have fueled frustration among CHP supporters, which spilled over into football stadiums at the weekend when fans chanted at top Istanbul derby matches for the mayoral mandate to be given to their candidate.
After the latest AKP comments on Tuesday, the lira weakened to 5.8250 against the dollar, it weakest since March 22, bringing its losses this year to 9 percent.The AKP has already lost control of the capital Ankara, as well as other key cities. Defeat in Istanbul, where Erdogan was mayor in the 1990s, would be an even greater blow to the president.