The U.S.-backed Syrian Democratic Forces (SDF) said Turkey would face "the appropriate response" if it follows through on a threat to widen its assault against a Syrian Kurdish militia all the way to the border with Iraq.
Senior SDF official Redur Xelil was responding to Turkish President Tayyip Erdogan's threat to sweep militants from the length of Turkey's Syrian frontier.
"When he tries to widen his battle, he will be met by the appropriate response," Xelil told Reuters in an interview in the town of Amuda in northern Syria.
Turkey launched an offensive six days ago against the Kurdish YPG militia in Syria's northwestern Afrin region. It regards the YPG, the strongest militia in the SDF, as a terrorist group.
Xelil said he was sure the U.S.-led coalition that has backed the SDF's battle against Islamic State (IS) militants in Syria was trying to put pressure on Turkey to limit its assault.
While U.S.-led coalition forces are present in other areas the SDF holds in Syria along the border with Turkey east of Afrin, they are not present in Afrin itself.
More than 66 civilians have been killed in Turkish air and artillery bombardments of Afrin, Xelil said, accusing it of committing war crimes.
Turkey considers the YPG to be an extension of the outlawed Kurdistan Workers Party (PKK), which has waged a three-decade-long insurgency in Turkey's largely Kurdish southeast. Washington regards the YPG as an effective partner in the fight against IS in Syria.