Turkish forces not yet involved and the campaign is being carried out by Turkish-backed Free Syria Army rebels, President Recep Tayyip Erdogan says.
Turkish President Recep Tayyip Erdogan said on Saturday "a serious operation" was beginning in Syria's Idlib and a Syrian rebel 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," Erdogan said.
"Now this step has been taken, and it is underway," he said, adding that Turkish forces were not yet involved and that it was a rebel operation so far.
Turkish-backed Free Syrian Army (FSA) groups who play a major role in Operation Euphrates Shield 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.
Erdogan, who was speaking at his AK Party's 26th Consultation and Assessment meeting said that, "We will never allow the formation of a terror corridor along our Syrian border.
We are now in the process of taking further steps towards securing Idlib after expanding the Euphrates Shield Operation."
Erdogan said that Russia is backing the operation from the air and Turkish soldiers from inside the Turkish border.
Turkish Foreign Minister Foreign Minister Mevlut Cavusoglu on late Saturday also commented on the operation, saying Turkey aims to prevent conflict in Syria's northwestern Idlib.
"We reached an agreement in Astana. Why? We want to prevent conflict in these areas. That is to say a de-conflict zone," Cavusoglu said, speaking to reporters in Turkey's western Afyonkarahisar province.
"But now, our aim is to revive the Geneva process," he added.
The minister stated that intelligence units and troops will assess the situation on the ground and will take steps accordingly.
Cavusoglu also said in a phone call on Saturday with US Secretary of State Rex Tillerson the pair discussed situation in northern Iraq and Syria.
"We already discuss with Rex Tillerson varied topics once in 10 days. We have a good dialogue," Cavusoglu said.
TRT World's Caitlin McGee looks at the latest.
Earlier on Saturday, Turkey continued to build up its number of troops on the southern border with Syria, close to the earmarked de-escalation zone near the city of Idlib.
Last month, Turkey agreed with Iran and Russia to establish de-escalation zones in northwestern Syrian province as part of the Astana peace deal.
The joint mission aims to promote an end to conflict in the region, fight al-Qaeda-linked Jabhat Fateh al Sham and Daesh.
TRT World's Sara Firth, who's in Reyhanli in Hatayi province, near the Turkey-Syria border, explains the latest efforts to build safe zones in northern Syria.
Focus on Hayat Tahrir Al Sham
Idlib had been a centre of fighting between Russia and Iran-backed regime forces and Turkey-backed opposition forces until July this year when Hayat Tahrir Al Sham took control of a large part of the province.
Hayat Tahrir Al Sham alliance is led by Jabhat Fateh al Sham, or the Nusra Front, which publicly shed its status as al Qaeda's Syrian affiliate in 2016 and rebranded to head the Hayat Tahrir al Sham amalgam.
The US maintains that the group is still linked to al Qaeda, however.
The alliance controls most of the northwestern province of Idlib after expelling former allies earlier this year.
The group on Saturday decried the operation saying it would "not be a picnic" for the FSA.
"The lions of jihad and martyrdom are waiting to pounce on them," it added in a statement posted on a social media site.
Idlib has strategic importance for all parties involved in Astana deal, and has shown little signs of de-escalation.
Earlier this week, sources from Turkey-backed opposition in Idlib, who spoke to TRT World on condition of anonymity, said that Iranian observers will be positioned along the southern borders of Idlib to create a practical buffer zone between Syrian regime forces and the opposition forces.
TRT World's Andrew Hopkins has more from Turkey's capital, Ankara.
Air strikes kill over a dozen civilians
Two waves of air strikes on Idlib killed at least 13 civilians over the past 24 hours, a Britain-based monitoring group said on Saturday.
Four children were among the dead in the early morning strikes on the Idlib province town of Khan Sheikhun on Friday and Saturday, the Syrian Observatory for Human Rights said.
Observatory chief Rami Abdel Rahman said the strikes were probably carried out by the Syrian regime air force, which has been carrying out an intensifying bombing campaign against opposition targets in Idlib province alongside aircraft from ally Russia.