By Huseyin Hayatsever and Ali Kucukgocmen
ANKARA (Reuters) -Turkey's anti-immigrant Victory Party leader endorsed opposition presidential candidate Kemal Kilicdaroglu on Wednesday, potentially boosting the challenger as he aims to make up ground and defeat President Tayyip Erdogan in Sunday's runoff election.
Umit Ozdag, head of the nationalist Victory Party that received 2.2% support in the May 14 parliamentary vote, urged supporters to back Kilicdaroglu in the May 28 runoff in which Erdogan seeks to extend his two-decade rule.
"We have decided to support Mr. Kilicdaroglu in the second round of the presidential elections," Ozdag said at a news conference in Ankara alongside Kilicdaroglu.
The endorsement could counter-balance one that Erdogan received on Monday from Sinan Ogan, the presidential candidate of the far right alliance led by the Victory Party.
Ogan came in third with 5.2% of the presidential vote, behind Erdogan with 49.5% and Kilicdaroglu with 44.9%.
The race for endorsements from the right reflects the larger-than-expected support for nationalists on May 14. Analysts say many remain undecided, holding a possible key to victory in the runoff.
Ozdag said that his party and Kilicdaroglu agreed on a plan to send back migrants within a year "in line with international law and human rights."
Ozdag said he held similar talks with Erdogan's AK Party (AKP) but decided not to endorse him because their plans did not involve repatriating migrants.
Erdogan's strong showing in the initial vote confounded pollsters who had said Kilicdaroglu led opinion polls.
His AKP-led coalition won a majority in parliament, giving Erdogan another edge in one of Turkey's most consequential elections ever. Erdogan has said a vote for him in the runoff is a vote for stability.
Last week, Kilicdaroglu, head of the Republican People's Party (CHP) and candidate of a six-party alliance, sharpened his tone and vowed to repatriate all migrants once elected.
Turkey is the world's largest host of refugees, with some 5 million migrants, of whom 3.3 million are Syrians, according to Interior Ministry data.
Kilicdaroglu has also pledged to roll back much of Erdogan's sweeping changes to Turkish domestic, foreign and economic policies, including reversing an unorthodox economic programme to address a cost-of-living crisis.
For Kilicdaroglu's endorsement, his Republican People's Party (CHP) and the Victory Party also signed a protocol laying out key principles of their cooperation.
As part of the fight against terrorism, mayors would be replaced with state-appointed trustees with court rulings in case there is legal proof that they have terror links, according to the protocol.
The protocol could draw the ire of the pro-Kurdish HDP, which ran under the banner of the Green Left Party (YSP) due to a court closure case for alleged terror links and strongly backed Kilicdaroglu.
Most mayors elected from the HDP in local elections in 2019 were replaced by state-appointed trustees after they were jailed pending trial on terrorism charges.
The HDP and YSP executive boards said after meeting to discuss the deal that the article on trustees was "against universal democratic principles". The parties, whose support is crucial for Kilicdaroglu, said they were still evaluating their stance and would announce their decision on Thursday.
Kilicdaroglu's six-party alliance vowed to end the practice of replacing mayors with government-appointed trustees in its programme, stressing that elected officials will remain in office unless they are convicted by a court decision.
Ozdag is a former deputy leader of the nationalist MHP, which is in Erdogan's alliance. He later joined the IYI Party, which is in Kilicdaroglu's alliance, before being ousted and founding the Victory Party in 2021.