The AKP won 44.8 percent of the vote in Ankara to the CHP's 43.9 percent, according to provisional results on Turkish television. Angry crowds gathered at CHP headquarters late on Sunday claiming fraud, as it became clear their candidate had failed to win one of the closest races in the nationwide polls.

"Today we will be preparing our application for an appeal by comparing the minutes from the ballot boxes and data from the Supreme Electoral Council," the CHP's mayoral candidate for Ankara, Mansur Yavas, said on his Twitter account.

A CHP official said an appeal would be lodged later on Monday or on Tuesday. A second official said the party would also appeal the result in the southern coastal city of Antalya, traditionally a CHP stronghold, which fell to the AKP.

The vote turned into a referendum on Erdogan's rule amid corruption allegations and a stream of damaging security leaks. The opposition had hoped to inflict a deeper wound by taking either Istanbul or Ankara, but the AKP was able to hold both and increase its national share of the vote from 39 percent in 2009.

The Supreme Electoral Board said it could take weeks to announce final official results of the nationwide polls as it considers appeals, although no major changes to the figures reported by Turkish television stations are expected.

With about 98 percent of votes counted, the AKP, in power since 2002, had 45.6 percent of the vote nationwide, while the CHP trailed with 28 percent, according to the TV stations.

"We're going to reject Antalya and Ankara but as the electoral board has said they won't accept any major changes, we're not expecting much," the second CHP official said.

Erdogan declared victory after the elections and said he would "enter the lair" of enemies who have accused him of corruption and leaked state secrets. "They will pay for this," he said.

RA/NJF