The votes saw the AKP winning a narrow majority nationwide, but the opposition CHP scoring big in the large cities, and the pro-Kurdish HDP virtually sweeping Kurdistan.
"If there is one invalid vote in each ballot box, it makes 31,136 votes in total, which is more than the difference [between the two sides]", he said, adding that there are some 315,500 invalid votes in the polls.
Last year, after Mr Erdogan announced the June 24 parliamentary and presidential elections, the Council of Europe Parliamentary Assembly Monitoring Committee voiced concern over the freedom and fairness of Turkish snap elections and recommended they be postponed.
Neither Ankara nor Istanbul have been controlled by a party other than the AKP or its predecessor the Welfare Party (RP) since 1994.
The secularist Republican People's Party (CHP) overcame overwhelming media support for the AKP and an environment which European observers said fell short of requirements for "genuine democratic elections".
Sezgin Tanrikulu, a CHP MP from Istanbul, said that although Imamoglu won the race in Istanbul, the election board was waiting for the objection period to end for legal reasons to declare the official victor.
Anadolu said the AKP would appeal in some Ankara districts.
"But we do take the fact that many parties have been successful as a positive sign of Turkey's democratic resilience", he told reporters in Ankara.
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Parker said: "While it's still mathematically possible we won't give up, but I'm a realist and we all understand the predicament ahead".
Following the last week's prediction of JPMorgan, there had been intense volatility on the USD/Turkish Lira pair throughout last week and the Turkish currency had weakened as far as 5.6750 against the American dollar, which eventually had brought back memories of last year's currency crisis.
People walk past by AK Party billboards with pictures of Turkish President Tayyip Erdogan and mayoral candidate Binali Yildirim in Istanbul, Turkey, April 1, 2019.
In Istanbul, the county's largest city, the CHP mayoral candidate was more than 25,000 votes ahead of his AKP opponent as the last votes were being counted, according to the country's electoral board and CHP data.
"If (Erdogan) can not create a solution, it's inevitable that there will be greater losses in the period ahead", another party source said. The possibility of losing Istanbul, where he launched his political career and served as mayor in the 1990s, was an even greater shock.
The lira tumbled nearly 30 percent against the dollar a year ago and Turkey's economy has tipped into recession.
Over the past year, Erdogan has faced ire for an economic recession which heralds double-digit inflation, rising costs of living and high unemployment.
Erdogan acknowledged setbacks in a speech to his supporters, saying his party would work to understand what had gone wrong and fix the problem.
Andrew Dawson, head of the Council of Europe's election observation mission, said Monday his monitors were "not fully convinced that Turkey now has the free and fair electoral environment which is necessary for genuinely democratic elections".