By Huseyin Hayatsever and Jonathan Spicer
ANKARA (Reuters) -The man challenging for the Turkish presidency has accused President Tayyip Erdogan of being a "fabricator" after he cited a doctored video to allege opposition links to an outlawed militant Kurdish group ahead of a runoff election on Sunday.
Erdogan repeated the allegation and referred to the doctored video, splicing footage of Kemal Kilicdaroglu and a Kurdish militant, in an interview with state broadcaster TRT late on Monday, despite having been criticised by the opposition for showing it earlier in his campaign.
The origins of the video are unknown.
Responding in a Tweet, Kilicdaroglu said: "I am tired of being slandered, but he is not tired of slandering me."
Opponents of Erdogan see the accusations as a symptom of a media landscape tilted heavily in Erdogan's favour after a decade of transformation, imprisonment of journalists and closures of critical outlets. This they say has presented voters with a different reflection of reality ahead of the election.
Reporters Without Borders ranks Turkey 165th out of 180 countries for press freedoms.
Erdogan's allegations have added to political tension ahead of the runoff, in an election seen as the stiffest test yet for the president, who is seeking to extend his rule into a third decade.
Though his standing has been hit by a cost-of-living crisis, Erdogan emerged ahead of Kilicdaroglu in the first round.
Seeking to tap nationalist sentiment, Erdogan has repeatedly suggested links between the Kurdistan Workers Party (PKK)and the opposition, without providing evidence.
The doctored video, screened by Erdogan at a May 7 rally, comprises footage taken from a Kilicdaroglu campaign video and PKK images from a video released online 10 months ago in which the militants cheer their top commander, Murat Karayilan.
Referring to the video in his interview on Monday, Erdogan once again accused Kilicdaroglu of cooperating with the PKK, deemed a terrorist group by Turkey and its Western allies, and which has been waging an insurgency since 1984 in which more than 40,000 people have been killed.
"Kilicdaroglu shot videos with terrorists in Qandil," Erdogan said, referring to a PKK base in Iraq's Qandil mountains. "Doctored or not, they shot videos with those in Qandil, and PKK members showed their support to Kilicdaroglu with videos," he said.
Kilicdaroglu, in his response on Twitter, declared Erdogan a "fraudulent (video) fabricator." Scores of influential social media users also expressed their anger, with "montaj" (montage) trending #4 on Twitter in Turkey on Tuesday afternoon.
Erdogan emerged ahead of Kilicdaroglu in the first round on May 14. On Monday, Erdogan received another boost to his reelection campaign by winning the endorsement of a hardline nationalist who came third.
Responding to Kilicdaroglu in a tweet, Fahrettin Altun, the Turkish presidency communications director, accused him of insulting the president. The people would "teach a lesson" to those who insult Erdogan, he said.
Emre Kizilkaya, chair of the Vienna-based International Press Institute's (IPI) national committee in Turkey, said that Turkey has been subjected to "an unparalleled level of organised disinformation" throughout the recent election campaign.
"Truth and factual information have come under a coordinated assault from multiple sources, with the government playing a central role in this troubling phenomenon, as evidenced by Erdogan's tactics to tarnish the opposition through various channels", he said.
Kilicdaroglu has the backing of a six-party alliance, in addition to the endorsement of the pro-Kurdish HDP Party - which is facing a potential ban over links to the PKK, which it denies. Erdogan frequently accuses the HDP of such ties.
(Reporting by Huseyin Hayatsever and Jonathan Spicer; Editing by Tom Perry, Alexandra Hudson)