Kemal Kilicdaroglu, the main election rival of Turkish President Tayyip Erdogan, issued a warning to Russia, accusing it of responsibility for the release of fake material on social media ahead of Sunday's ballot.
Kilicdaroglu, who has a slight lead over long-time leader Erdogan according to opinion polls, did not specify to which material he referred.
A third presidential candidate, Muharrem Ince, withdrew from the race on Thursday citing a faked "character assassination" carried out online. He gave few details.
Kilicdaroglu accused Turkey's "Russian friends" of responsibility for "the release in this country yesterday of montages, plots, deep fake content…
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"If you want to continue our friendship after May 15, withdraw your hand from the Turkish state. We are still in favour of cooperation and friendship," he said on Twitter on Thursday evening in both Turkish and Russian.
There was no immediate comment from Russian officials.
Moscow and Ankara have close ties and Russia is Turkey's largest supplier of energy. President Vladimir Putin and Erdogan hold frequent talks on issues ranging from energy to the wars in Ukraine and Syria.
In the tense campaign ahead of the May 14 presidential and parliamentary votes, political figures from both the Erdogan and Kilicdaroglu camps have complained about online accusations, including the posting of videos and photographs.