"Now this step has been taken, and it is under way".

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

HTS has pledged to keep fighting Syrian regime forces and their allies, casting doubt on the de-escalation agreement, but Ankara has worked to lure militants from it, and two groups have defected from the alliance.

The operation is led by Turkish-supported Free Syrian Army rebels.

In the city's central districts security will be provided by the Turkish Armed Forces, while Russia's Armed Forces will ensure safety on the outskirts, according to the president.

Appearing to confirm this, Erdogan said: "Idlib is a region where we will provide protection in the inside and Russian Federation on the outside". "We expect that the large-scale operation that has been prepared will be launched perhaps within the next 24 hours", the rebel said.

The Turkish president has announced plans to start a new military operation in Syria in a move which has been rumored for weeks.

Idlib had been a centre of fighting between Russian Federation 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.

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 and has "categorically rejected" the implementation of a de-escalation zone.

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

"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".

President Recep Tayyip Erdoğan has announced Turkey is conducting a "serious" operation against extremist groups in Syria's northwestern Idlib province with anti-Assad rebels.

"When you enter a boxing match, you don't count how many punches you throw", he 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 a rebel operation so far.

In July Tahrir al-Sham seized land around the Bab al-Hawa border crossing between Syria and Turkey, bringing much of the frontier area inside Syrian under its control.