"The FSA has to know that their enemy is not in Ras Al Ain and in other Kurdish areas. Their enemy is in Aleppo and Damascus, so why don't you go there to attack your real enemy?" said Omar Aloush, a top official in the Kurdish Democratic Union Party, the Syrian wing of the PKK.
Speaking by phone from the Kurdish-controlled Syrian town of Qoubani, Aloush said his Kurdish faction would not use force to push Syrian rebel groups out of Ras Al Ain. But he warned that his movement could withhold food and other supplies to put pressure on the rebels.
The threats were met with defiance by a rebel media activist in Ras Al Ain.
"We don't care if the Kurds say you have to leave," said Yalmaz Basha of the FSA. "All Syrians have to sacrifice, even the Kurds, because they are part of the Syrian people."
The simmering tensions between Kurdish militiamen and the FSA have exploded in deadly violence within the past month in the embattled northern city of Aleppo.
They also underscore the difficulties foreign powers face trying to unify Syria's opposition, while trying to hasten the downfall of Syrian president Bashar al-Assad.
On Friday, the Turkish government once again denounced the Syrian regime, claiming it had no legitimacy.
Turkish Foreign Minister Ahmet Davutoglu then announced his government would be recognizing a newly formed Western-backed opposition movement known as the National Coalition Forces of the Syrian Revolution as "the legitimate representative of the Syrian people."
But Turkey has failed to deter the Syrian military from carrying out operations within sight of the Turkish border.
On Friday, Syrian and Turkish witnesses told CNN they saw Syrian government aircraft bombing targets near the Bab el Hawa border get between the two countries.