By Huseyin Hayatsever, Ali Kucukgocmen and Burcu Karakas
ANKARA (Reuters) - Tayyip Erdogan's rival in Turkey's presidential race accused the government on Wednesday of allowing 10 million "irregular" migrants to enter the country, marking a nationalist turn in his rhetoric ahead of a May 28 runoff vote.
Kemal Kilicdaroglu, candidate of a six-party opposition alliance, trailed Erdogan in the first round of the presidential election held on Sunday, confounding expectations in opinion polls that he would come out ahead.
Kilicdaroglu's latest comments came after his party said it had filed complaints over suspected irregularities at thousands of ballot boxes in Sunday's landmark elections.
Erdogan's ruling Islamist-rooted AK Party and its nationalist allies won a comfortable parliamentary majority in Sunday's elections, while Erdogan fell just shy of the 50% threshold needed to win outright in the presidential contest.
Kilicdaroglu, chair of the secularist Republican People's Party (CHP), received 44.9% in what was seen as the biggest electoral challenge to Erdogan's 20-year rule.
A third candidate, nationalist Sinan Ogan, obtained 5.17% and both Erdogan and Kilicdaroglu are expected to seek his endorsement in negotiations this week.
"We will not abandon our homeland to this mentality that allowed 10 million irregular migrants to come among us," Kilicdaroglu said in a video posted on Twitter on Wednesday, warning the number of migrants could go up to 30 million.
"Those who love their homeland, come to the ballot box," Kilicdaroglu urged voters.
He provided no evidence regarding the number of migrants. Turkey hosts the world's largest refugee population of around 4 million, according to official figures.
Turkish authorities have caught nearly 50,600 irregular migrants this year as of May 11, after apprehending some 285,000 in 2022, according to Interior Ministry data.
Kilicdaroglu's nationalist-flavoured video suggested that his campaign was departing from its previous more moderate stance.
It could also be seen as appealing to supporters of Ogan, who had campaigned on sending back migrants, including some 3.6 million Syrians displaced by war to the south.
Erdogan, now in pole position, says only he can ensure stability in Turkey, a NATO member state, as it grapples with a cost-of-living crisis, soaring inflation and the impact of devastating earthquakes in February.
Analysts have said Erdogan's insistence that the opposition was backed by Kurdish militants - using fabricated videos and without any evidence - had chimed with his voter base, outweighing their economic worries.
His message was an allusion to the pro-Kurdish Green Left Party (YSP), which backed Kilicdaroglu but was not part of the six-party opposition alliance.
The YSP, which is the third largest party in the new parliament after Erdogan's AKP and Kilicdaroglu's CHP, denies ties to the Kurdish militants.
Mehmet Ali Kulat, chairman of MAK polling company, said that for many voters the opposition did not appear sufficiently tough on terrorism.
"The government made voters answer this question: 'Okay, you lost some of your wealth and resources but do you want to lose your state too?" Kulat said.
In Wednesday's video, Kilicdaroglu also accused Erdogan of cooperating with the network Ankara accuses of orchestrating a 2016 coup attempt. The network is classed in Turkey as a terrorist organisation.
Metropoll pollster Ozer Sencar said the opposition alliance had created a fractured image due to internal disputes.
"They damaged their reputation," he said.
MAK's Kulat said a majority of voters in the 11 provinces hit by the earthquakes had also mostly supported Erdogan because they believed he was best placed to rebuild devastated cities.
Separately on Wednesday the CHP said it had filed complaints over suspected irregularities at thousands of ballot boxes in the elections, though party officials said the objections were unlikely to alter the overall result of the presidential vote.
(Additional reporting by Ali Kucukgocmen in Ankara; Editing by Jonathan Spicer and Gareth Jones)