BEIRUT/ANKARA/KOBANI, Syria: Turkey’s military has begun setting up observation posts in northwest Syria’s militant-controlled Idlib province, its General Staff said Friday, in a bid to stop the fighting there. 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.”

Turkey sent a convoy of about 30 military vehicles into rebel-held northwest Syria through the Bab al-Hawa crossing in Idlib, rebels and a witness said.

Video distributed by the Turkish army showed what it said was the convoy starting to move Thursday night, with military vehicles travelling along a road in darkness.

Turkey says its operation, along with Syrian rebel groups it backs, is part of a deal reached last month with Russia and Iran in Astana, Kazakhstan, to reduce fighting between rebels and the Syrian government.

The army said its forces in Syria were conducting operations in line with rules of engagement agreed with Russia and Iran.

Idlib is largely controlled by Hay’at Tahrir al-Sham, a group led by Al-Qaeda’s former Syria affiliate, which has ousted more moderate rebels in recent months.

However, the deployment is also intended to rein in the Kurdish YPG militia, which holds the adjacent Afrin region, a senior rebel official involved in the operation said.

“[It is] in line with Astana six resolutions to ensure the area is protected from Russian and regime bombing and to foil any attempt by the separatist YPG militias to illegally seize any territory,” said Mustafa Sejari, an official in a Free Syrian Army rebel group.

Broadcaster CNN Turk reported on its website that there was a clash in the Idlib countryside near the Ogulpinar border post in Turkey’s Reyhanli district.

It said the sound of “doshka” (machine-gun) fire from across the border could be heard in Reyhanli district and it was not clear which forces were clashing.

The convoy was heading toward Sheikh Barakat, a high area overlooking rebel-held territory and the Kurdish YPG-controlled canton of Afrin, the witnesses said.

President Recep Tayyip Erdogan announced the deployment on Saturday, saying Turkey was conducting a “serious operation” with rebel groups it supports.

Sejari, the rebel official, said it was important to contain the YPG to prevent any new military offensive to reach the Mediterranean, something that would require it to capture swathes of mountains held by rebels and Syria’s army.

“Today we can say that the dream of the separatists to reach the sea and enter Idlib and then to Jisr al-Shaqour and the coastal mountains has become a dream,” he said

Turkey regards the YPG as an extension of the PKK, a Kurdish group inside Turkey that has been waging armed insurgency against Ankara for three decades.

“We said we may come unannounced one night, and tonight our armed forces started the operation in Idlib with the Free Syrian Army,” Erdogan said Friday in a speech to his AK Party.

“We are the ones with the 911 kilometer border with Syria, the ones who are constantly under threat,” he added, noting the YPG’s presence in Afrin.

As the strongest part of the Syrian Democratic Forces, the YPG has received military aid from Turkey’s NATO ally the United States to fight Daesh (ISIS).

Last year, Turkey launched the Euphrates Shield operation, an incursion into northern Syria alongside Syrian rebel groups to take territory on the frontier from Daesh.

That operation was also aimed at stopping the YPG using its own advances against Daesh to link Afrin with the much larger area it controls in northeastern Syria.

In the area taken by the Euphrates Shield campaign, Turkey has made changes to local governance that indicate it may be laying a foundation for long-term ties with that part of Syria.

The Astana agreement with Assad’s foreign allies Russia and Iran involves reducing fighting in several regions of Syria, including Idlib and adjacent swathes of the northwest, the most populous rebel-held area.

In other developments, the Russian military says its warplanes have flown hundreds of sorties against Daesh in eastern Syria.

Col. Gen. Sergei Rudskoi of the military’s General Staff said Friday that Russian jets have flown 383 missions in the area of Deir al-Zor alone over the past week, hitting 993 Daesh targets.

He said Friday that the Syrian army has been successfully developing its offensive on the eastern bank of the Euphrates River.

Rudskoi said Daesh counterattacks involving over 1,000 militants who moved from Iraq have been repelled. He added that the Syrian troops are working to clear the town of Mayadeen from militants.

He also said the zone under Daesh control has shrunk to 14,800 square kilometers, or less than 8 percent of Syria’s territory.

Meanwhile, talks on securing safe passage for civilians from Raqqa have stopped, a city official close to the discussions told AFP Friday.

A new video that emerged Friday shows desperate, terrified residents emerging from destroyed districts, some of them collapsing on the ground in exhaustion as they arrive. They seemed to be taking advantage of a slowdown in the fighting and airstrikes by the U.S.-led coalition amid efforts to ensure the safe evacuation of an estimated 4,000 civilians who remain trapped in the city.

Some of the arriving men were searched before being allowed in while others kissed the ground in relief.