Turkey's opposition leader vowed Thursday to send back millions of migrants in a strident message aimed at winning the backing of an ultra-nationalist who helped push last weekend's presidential vote to a runoff, AFP reported.

Secular opposition leader Kemal Kilicdaroglu delivered his first public address since a landmark election Sunday in which he came in almost five points behind President Recep Tayyip Erdogan.

Kilicdaroglu's performance was the opposition's best of the Turkish leader's two-decade rule.

But it fell short of expectations set by pre-election polling and left the opposition visibly depressed.

The 74-year-old has since revamped his campaign team and toughened his message to win over Turkey's right-wing voters in the May 28 runoff.

He also plans to meet Sinan Ogan -- a far-right figure who picked up 5.2 percent of the vote and is still weighing his endorsement.

Kilicdaroglu tried Thursday to toughen his message considerably from the more inclusive tone he set in the first stage of the campaign.

"Erdogan, you did not protect the borders and honor of the country," the former civil servant said.

"You have deliberately brought more than 10 million refugees to this country... As soon as I come to power, I will send all the refugees home."

Ogan has said he will only back a candidate who cracks down on migrants and fights "terrorism" -- a code word in Turkey for Kurdish militants.

- 'Syrians are our brothers' -

Erdogan and his party were lionized across swathes of the Muslim world for their more embracing stance towards those fleeing conflicts in countries such as Syria.

Turkey's five-million-strong refugee and migrant population became the world's largest in the past decade.

A separate 2016 deal between Ankara and the European Union helped stem the continent's migrant crisis by allowing those trying to reach Western Europe to settle in Turkey.

Turkey won billions of euros in funding from Brussels for the program.

But an economic crisis that gathered pace as the election neared sent anti-migrant sentiment soaring.

Erdogan's government has tried to find a middle ground.

Interior Minister Suleyman Soylu said on Thursday that Turkey had already sent more than half a million Syrians back.

"We are not going to make Turkey into a refugee warehouse, and we have not done so to date. But the Syrians are our brothers," Soylu said.

"We cannot send them to their deaths. And we have not. Tayyip Erdogan doesn't want to be remembered as a leader who sent Syrians to their deaths."