If the U.S. armed the PKK/PYD, “the U.S. becomes a country that supports extremism. Let me caution them. We are speaking as a friend," Cavusoglu told news channel A HABER.

If it armed the PKK/PYD, "it becomes a country that cooperates with extremists and works with the extremists,” he added. 

Cavusoglu was responding to remarks in Sunday’s presidential debate, in which Democratic candidate and front-runner Hillary Clinton said she would consider arming Kurdish fighters – widely seen as a reference to the armed wing of the PYD, the Syrian offshoot of the PKK, listed as a extremist organization by Turkey, the U.S., and the EU.

The PKK has fought a three-decade war against Turkey in which more than 40,000 people have died. 

"I would also consider arming the Kurds," Clinton said, when asked how she would deal with Syria. "The Kurds have been our best partners in Syria, as well as Iraq. And I know there’s a lot of concern about that in some circles but I think they should have the equipment they need so that Kurdish and Arab fighters on the ground are the principal way that we take Raqqah after pushing ISIS [ISIL] out of Iraq."