People's Protection Units (YPG) terrorists emptied a prison in northeast Syria holding Daesh militants before Turkish troops arrived in the area, Defense Minister Hulusi Akar said.

Speaking to reporters in Ankara on Monday, Akar said the prison in Tal Abyad district center was the only one holding Daesh militants that Turkish forces had so far reached in the envisaged "safe zone" area.

"As you know, there is a prison issue on this Daesh topic. We are determined to show the utmost effort on these prisons. However, there was only one prison in our region, a Daesh prison," Akar said.

"When we went there, we saw that it had been emptied by the YPG and the Daesh militants there had been abducted. We determined this through photographs and film, talked to our counterparts, and will continue to do so," he added.

Akar did not say how many prisoners were believed to have been taken from the jail, nor did he elaborate on who had taken the prisoners and where.

Turkey launched Operation Peace Spring, the third in a series of cross-border anti-terror operations in northern Syria targeting terrorists affiliated with Daesh and the PKK's Syrian offshoot the YPG, on Oct. 9 at 4 p.m.

The operation, conducted in line with the country's right to self-defense borne out of international law and U.N. Security Council resolutions, aims to establish a terror-free safe zone for Syrians return in the area east of the Euphrates River controlled by the U.S.-backed Syrian Democratic Forces (SDF), which is dominated by YPG terrorists.

The PKK — listed as a terrorist organization by Turkey, the U.S. and the European Union — has waged a terror campaign against Turkey for more than 30 years, resulting in the deaths of nearly 40,000 people, including women, children and infants.

Turkey has long decried the threat from terrorists east of the Euphrates in northern Syria, pledging military action to prevent the formation of a "terrorist corridor" there.

Since 2016, Turkey's Euphrates Shield and Olive Branch operations in northwestern Syria have liberated the region from YPG/PKK and Daesh terrorists, making it possible for nearly 400,000 Syrians who fled the violence to return home.