Turkey's president vowed to oust Kurdish militants from Afrin, northern Syria, on Saturday as Syrian rebels also said they are bracing for such an operation.
Speaking in the eastern province of Elazig, President Recep Tayyip Erdogan warned the People's Protection Units, or YPG, that Turkey will intervene if the "terrorists in Afrin do not surrender."
His remarks came as Turkey's military shelled Afrin, a Kurdish-controlled enclave along Syria's frontier with Turkey, saying it was responding to harassment by the YPG, according to the Turkish station NTV.
Turkey regularly shells Afrin but Saturday's assault was particularly intensive and lasted more than two hours, said YPG spokesman Rojhat Roj.
"We are seeing preparations" for a Turkish push into Afrin, said Roj.
"The YPG will defend itself against any aggression," he added.
Turkey considers the YPG a terror group and an extension of the Kurdish insurgency within its own borders.
The YPG and its political counterpart, the Democratic Union Party, or PYD, say they want regional autonomy within a federalized Syria.
They control nearly 25 percent of Syrian territory, shrewdly striking alliances with the U.S. and Russia to establish the Kurds as a powerful force on the ground in Syria's civil war.
But the Afrin region is detached from the bulk of Kurdish-controlled territory in northeast Syria. It's surrounded on three sides by Turkish forces and Syrian rebels backed by Ankara. And while the U.S. military maintains bases in the Kurdish territory in northeast Syria, it is not believed to be present in Afrin.
A Syrian opposition news site, Baladi News, quoted a rebel commander on Thursday as saying that joint Turkish military and Syrian rebel operations to attack Afrin could begin "at any moment."
Moaz Abu Omar of the Failaq al-Sham rebel faction said ground operations would likely be backed by Turkish air power.
Turkey has already stationed troops and armored vehicles in rebel-held territory on either side of Afrin in northern Syria. The Turkish military entered rebel-held Idlib in October to monitor "de-escalation zones" between rebels and the Syria government, following an agreement with Russia and Iran to restore order in Syria.
Kurdish officials say the Turkish deployment is a cover for operations against them.
"The Turkish government needs to realize a military operation will not succeed," said Kurdish political official Rezan Hiddo. The YPG is reporting artillery strikes to Russian military observer units stationed in Afrin, he added.
Erdogan has repeatedly said that Turkey will not allow Kurdish militants to form a "terror corridor" in northern Syria.
"They will see how we will mess them up in not even a week," said Erdogan on Saturday.