Kemal Kilicdaroglu, the main opponent of Recep Tayyip Erdogan in the presidential elections to be held on May 14, on Thursday accused Russia of resorting to a "deep rigging technique" in the context of the electoral campaign.

Kilicdaroglu's accusations came hours after another candidate, Muharrem Ince, announced his withdrawal from the electoral race after becoming the target of an online defamation campaign.

"Dear Russian friends, you are behind the montages, conspiracies, forgeries and recordings that were exposed yesterday in this country," Kilicdaroglu wrote on Twitter.

He added, "If you want our friendship after May 15, do not touch the Turkish state. We always support cooperation and friendship."

Opinion polls show the secular opposition leader slightly ahead of Erdogan in Sunday's presidential elections. If none of the candidates receives more than 50% of the vote, a second round will be held on May 28.

On Thursday, the head of the "Watan" party, Muharrem Ince, announced his withdrawal from the presidential race, after he became the target of a defamation campaign on the Internet, which included, in particular, fake photos of him accompanied by women or sitting behind the wheel of a luxury car.