"I condemn U.S. support for PYD and YPG. This is not the promise that was given to us," Erdogan said during an opening ceremony for a new terminal at Diyarbakir Airport in eastern Turkey.
He was speaking after Turkey expressed outrage at pictures showing members of U.S. special forces in Syria wearing YPG insignia and patches.
Erdogan said: "I believe that the politics must be done honestly. Thus, the friends who believe in us and the ones who stand with us in NATO should not and cannot send its own soldiers to Syria with YPG patches.
"The ones who say: 'We will continue to support the YPG, it is not the PKK',... you are on the wrong side.”
The YPG is the armed wing of the PYD -- the Syrian offshoot of the PKK, which is designated a terrorist organization by Turkey, the U.S. and the EU.
While Turkey views the PYD and YPG as terrorist groups, Washington continues to support the YPG as an "effective partner" in the fight against Daesh.
Prime Minister Binali Yildirim also attended the opening ceremony and said that Turkey had no “Kurdish problem” only a terrorism problem.
“The PKK does not care about Kurdish people’s problems. Your problems and Turkey’s problems are just the PKK terrorist organization. We are committed that that PKK should no longer a problem for us,” he said.
The PKK – listed as a terrorist organization by Turkey, the U.S. and EU – resumed its 30-year armed campaign against the Turkish state in July 2015.
Since then, nearly 500 members of the security forces, including troops, police officers and village guards have been martyred and over 4,900 PKK terrorists killed in operations across Turkey and northern Iraq.