Turkish President Recep Tayyip Erdoğan said on Saturday "a serious operation" was beginning in Syria's Idlib and a Syrian opposition official said his group was preparing to enter the area with the backing of Turkish forces.
"Today there's a serious operation in Idlib and it will continue, because we have to extend a hand to our brothers in Idlib and to our brothers who arrived in Idlib," Erdoğan said.
"Now this step has been taken, and it is underway," he said, adding that Turkish forces were not yet involved at that it was an opposition operation so far.
Russia is backing the operation from the air, Erdoğan said.
"We will never allow a terror corridor along our borders in Syria," he added. "We will continue to take other initiatives after the Idlib operation."
Turkey-backed Free Syrian Army (FSA) groups in the Euphrates Shield Operation that Ankara launched in northern Syria last year are ready to cross into northwest Syria from Turkey, Mustafa Sejari, a senior official in the Liwa al-Mutasem group said.
"The Free Syrian Army with support from Turkish troops is in full readiness to enter the area but until this moment there is no movement," he said.
Erdoğan said last month that Turkey would deploy troops in Syria's northwest Idlib province as part of a de-escalation agreement brokered by Russia in August.
Another FSA opposition member in the Euphrates Shield told Reuters he believed an incursion into northwest Syria was imminent.
The Hamza Brigade, also part of Euphrates Shield, posted video online of what it said was a convoy of its forces heading for Idlib.
Residents near the Bab al-Hawa border crossing with Turkey in Syria sent Reuters photographs of what they said was a section of the frontier wall being removed by the Turkish authorities.