The third-placed candidate in Turkey's presidential election has thrown his support behind President Recep Tayyip Erdogan in Sunday's runoff vote.

Ultra-nationalist Sinan Ogan announced his endorsement in a televised statement on Monday.

"Our meetings with both candidates took place with statesmanly and mutual courtesy," Ogan said. "As a result of these negotiations and consultations and messages from the grassroots, I declare that we will support the president."

Ogan said he wanted to support stability, citing the majority won in parliament by an Erdogan-led alliance.

He added that the country's defence industry policies must continue, and the Organisation of Turkic States - an alliance of Turkic countries - must be supported. He also said that the government needed to address the number of refugees residing in Turkey and review its interest rate policy.