Turkish armed forces would "never allow the establishment of a state in northern Syria", President Recep Tayyip Erdogan said on Friday.
Erdogan highlighted a "possible threat" near the Turkish border with Syria, while speaking in the southeastern province of Sanliurfa.
"Nowadays, there is some negative progress in Syria. If that would cause any threat to our borders, the world should know that we would react the same as we did in Operation Euphrates Shield," Erdogan said.
Turkey launched Operation Euphrates Shield last August to eliminate the Daesh presence in northern Syria. The operation ended in late March.
Led by Free Syrian Army (or FSA) fighters, the operation aimed to improve security, support coalition forces and eliminate the terror threat along the Turkish border.
"Unfortunately, our strategic partner countries are acting together with terrorist countries," Erdogan said.
"We told them to act against Daesh together. Can we not handle the business with nine coalition countries against Daesh? This PYD, YPG, are terrorist groups. They unfortunately insisted on going the other way."
The PKK/PYD is the Syrian offshoot of the PKK, designated a terrorist organisation by Turkey, the US and EU. However, the US views the PKK/PYD as its ground ally against Daesh and has armed the group despite objections by its NATO ally, Turkey.