Turkish President Recep Tayyip Erdogan says Ankara-backed Free Syria Army rebels have launched a major operation in northwestern Syria against former al-Qaeda-linked fighters.

The push on Saturday comes as Turkey along with Russia and Iran prepare to set up a so-called "de-escalation" zone in Idlib province, in line with deals in talks in Kazakhstan's capital, Astana, aimed at ending the Syrian civil war.

Idlib is largely held by the Hay'et Tahrir al-Sham alliance, which was not part of the talks and has rejected the implementation of a de-escalation zone.

READ MORE: Syria's civil war explained from the beginning

Erdogan said the operation, which has seen Turkish troops heading towards the border but not yet crossing it, was being conducted in coordination with Russia, an ally of Syrian President Bashar al-Assad.

"Today, there's a serious operation in Idlib and it will continue," Erdogan said in a televised speech.

''We have opened up a space in our region with operation Euphrates Shield and now we are making efforts to take a step forward by maintaining security in Idlib," he added.

Erdogan said many Syrians had fled to Idlib from neighbouring Aleppo province, which was rocked by heavy fighting last year, and Turkey was not going to let them down.

"We can't tell them, 'Whatever happens, happens. You can either die or survive.' We have to extend a hand to our brothers. Now, this step has been taken, and it is under way.''

'Not a picnic'

Idlib is mainly controlled by HTS, an alliance led by al-Qaeda's former Syria affiliate, which ejected more moderate rebels in recent months

HTS is not party to a deal brokered in Astana by Russia, Turkey and Iran for the safe zone in the province, one of four such "de-escalation" zones across Syria.

Removing HTS forces from the area will be needed to allow the arrival of Iranian, Russian and Turkish forces to implement a de-escalation zone.

In a statement posted on social media, the group accused the Turkey-backed factions of working with Russia and described them as traitors - but did not mention Turkey.

HTS said Idlib would "not be a picnic" for them and added "the lions of jihad and martyrdom are waiting to pounce".

Al Jazeera's Hashem Ahelbarra, reporting from Gaziantep near the Turkey-Syria border, said the operation was "definitely a significant move by the [Turkish] army" but more details were needed.

"We have to wait and see what the military planners of Russia, Iran and Turkey come up with, particularly when it comes to maintaining troops on the ground," he said.

Ahelbarra said the big question is what will be the reaction of HTS, which has thousands of fighters entrenched in different areas of the province.

"If they decide to put up resistance against this whole military operation I think in the coming days we are likely to see some of the most intensive fighting ever in Syria."

Commando units

Erdogan told reporters the operation was led by FSA rebels and that the Turkish army was "not yet" operating inside Syria.

State-run Anadolu news agency said there was a major build-up of fully-equipped commando units and military vehicles around the town of Reyhanli bordering Idlib close to the Cilvegozu border crossing.

The Hurriyet daily said ultimately Turkey would ensure security in Idlib city and Russia in the surrounding area.

Appearing to confirm this, Erdogan said: "Idlib is a region where we will provide protection in the inside and Russia on the outside."

The Britain-based Syrian Observatory for Human Rights (SOHR) monitor said Turkish army cranes had begun removing sections of the security wall Turkey has built on the border in preparation for an incursion. It said the operation was yet to formally begin.

Turkey earlier this year wrapped up its months-long Euphrates Shield operation in Aleppo province that involved both the Turkish army and Syrian rebels.

Asked whether the Idlib operation would be similar to Euphrates Shield, Erdogan replied: "When you enter the boxing ring you don't count your punches."

A rebel commander participating in the operation, who spoke on condition of anonymity, told AFP news agency in Lebanon's capital, Beirut, that "all the rebel groups" who took part in Euphrates Shield are participating in the latest operation.

"The fighters number in the thousands and there are Turkish soldiers participating," he added, without giving further details. "The goal of the operation is to liberate Idlib fully from Tahrir al-Sham."

Coordination with Russia

The move comes a week after Russian President Vladimir Putin held talks with Erdogan in Ankara, with both sides agreeing to push for the Idlib de-escalation zone.

After those talks, Putin declared the right conditions now existed to end the over six-year civil war that has killed hundreds of thousands of people since 2011.

The Russian defence ministry said Saturday some 120 ISIL fighters and 60 foreign mercenaries were killed in a series of Russian air raids in Syria over the past 24 hours.SOHR in the last week has repeatedly accused Syria and Russia of carrying out deadly air raids in Idlib province with heavy civilian losses.

Despite being on opposite sides of the conflict, Russia and Turkey have been working together intensely since a 2016 reconciliation deal ended a crisis caused by the shooting down of a Russian warplane over Syria.

Russia, along with Iran, is the key backer of President Bashar al-Assad and Moscow's military intervention inside Syria is widely seen as tipping the balance in the conflict. Turkey, however, has backed rebels seeking Assad's removal.

Commenting on the coordination with Russia, Erdogan said: "Relations with the regime is something looked after by Russia, and we have taken measures in other areas."