Turkey announced on Friday it had deployed dozens of soldiers in the Syrian province of Idlib as part of its efforts to establish a de-escalation zone to stop fighting in the largely militant-controlled northwestern region.

The deployment also appeared to be aimed at preventing the expansion of Syrian Kurdish militia backed by the United States, but considered by Ankara to be "terrorists".

Over 100 soldiers, including special forces, and 30 armoured vehicles entered Idlib, Turkey's Hurriyet daily reported on Friday, as it speculated more troops could be sent to the province over the next few days.

In a statement on Friday the military said that it had begun "activities to establish observation posts on October 12 (Thursday)".

Earlier, Turkey's armed forces said they had begun setting up observation posts in the province.

It said the Turkish forces in the region were carrying out their duties in line with rules of engagement agreed with Russia and Iran.

A first convoy crossed into the area late on Thursday, two rebels and a witness said.

The convoy included about 30 military vehicles, said Abu Khairo, a commander in a Free Syrian Army (FSA) rebel group based in the area, and it entered Syria near the Bab al-Hawa border crossing, according to a civilian witness.

Fighters from Hayat Tahrir al-Sham, an alliance of militant groups including the former al-Qaeda affiliate previously known as the Nusra Front, escorted the convoy, Abu Khairo said.

"The Turkish army convoy is entering under the protection of Tahrir al-Sham to take positions on the frontline with the YPG [People's Protection Units]," another FSA official in the area said.

It was heading to Sheikh Barakat, a hilltop that overlooks large areas of rebel-held northwestern Syria, but also the Afrin area held by the Kurdish YPG militia.

ANALYSIS: Turkey's Idlib adventure a last gasp bid to secure influence Read More »

Turkey said on Saturday it was carrying out a military operation in Idlib and surrounding areas as part of a deal it reached with Russia and Iran last month to enforce a "de-escalation" zone in northwest Syria.

The zone is one of several set up around Syria to reduce warfare between rebels, including groups backed by Turkey, and the government, which is supported by both Russia and Iran.

On Monday, the Turkish army said it launched a reconnaissance mission in Idlib.

"The Turkish armed forces began reconnaissance activities on 8 October (Sunday) to establish surveillance posts as part of the operation to be carried out in Idlib province," the armed forces said in a statement.

Hayat Tahrir al-Sham opposes the de-escalation deal with the government, but its role in escorting the Turkish reconnaissance team on Sunday indicated there might not be any direct military confrontation between its fighters and Turkey.

The Turkish military operation in Idlib will also include Syrian rebel groups involved in the Euphrates Shield operation that Ankara launched in Syria last year further to the east, Turkish President Tayyip Erdogan said on Saturday.

Hayat Tahrir al-Sham and Euphrates Shield rebels have fought previously and the militant alliance has this year battled other rebels in Idlib and surrounding areas in an effort to consolidate its control.

Turkey's decision to launch the Euphrates Shield campaign a year ago was aimed partly at pushing the Islamic State (IS) group from its border, but also at stopping the Kurdish YPG from gaining more sway.

Backed by the United States in its battle against IS, the YPG has seized much of northeastern Syria and was trying to link up that territory with its canton in Afrin.

Turkey regards the YPG as an extension of the Kurdistan Workers' Party (PKK) that it is fighting at home, and by gaining a presence in Sheikh Barakat, its forces would surround Afrin on three sides.

Several Turkish military vehicles, ambulances and tankers were visible in photographs published by Turkey's Anadolu news agency late on Thursday stationed at a village near Turkey's Reyhanli border gate opposite Bab al-Hawa.