Turkish President Recep Tayyip Erdogan accused the US Monday of "building an army of terror" on Turkey's border with Syria, state-run news agency Anadolu reported.
His comments came a day after the US publicly admitted it is supplying weapons and training to the Syrian Democratic Forces which include militia from the Kurdish YPG.
YPG fighters, many of them women, have played a major role in flushing out ISIS from northern Syria, including from Raqqa.
Turkey considers the YPG to be the Syrian arm of the PKK, an outlawed Kurdish group responsible for major terror attacks in the Turkey as part of its bid for national ethnic autonomy. The European Union and the US have both named the PKK as a terrorist outfit.
"The US has admitted to building an army of terror along our national borders," Erdogan reportedly told workers of a new sodium factory in Ankara. "It is our responsibility to suffocate this effort before it is born."
In his address at the opening of the Kazan Soda Electric Company, Erdogan also warned that the PKK will turn on its US sponsors at the drop of a hat.
"The name of this army should be the traitors' army," Erdogan was reported as saying. "As soon as this 30,000 strong terrorist army comes under threat, they will be the first to turn their guns on the American soldiers."
Coalition assisting to build Border Security Force
Sunday, US Army Col. Ryan Dillon, spokesman for the anti-ISIS Operation Inherent Resolve, said in a statement that coalition forces were working with the Syrian Democratic Forces (SDF) to establish and train the new Syrian Border Security Force (BSF).
"Currently, there are approximately 230 individuals training in the BSF's inaugural class, with the goal of a final force size of approximately 30,000," Dillon said.
He added that the idea was to train these defense forces in areas close to their homes. "More Kurds will serve in the areas in northern Syria. More Arabs will serve in areas along the Euphrates River Valley and along the border with Iraq to the south," he said.
Dillon said half of the planned 30,000 troops it will train were SDF veterans.
"These individuals will bring much-needed experience and discipline to the young force," Dillon said.
"To fill the other 15,000 positions, recruiting and training is underway. As previously mentioned, recruiting is being done in such a manner as to build a force reflecting the populations they serve."
'Do not stand between us and terrorists'
Erdogan added in his Ankara speech that Turkey has already raised its concerns about the new border force with Washington and its allies.
"What we have told all our allies and friends is this: do not stand between us and terrorists, between us and murderers, otherwise it may give rise to situations that are unwanted and we will not be responsible," he was reported as saying.
"Take down the flags you fly on terrorist bases so that we do not have to hand them back to you. Remove your signage from terrorist uniforms so we do not have to bury them on the ground with the terrorists," he said.