BEIRUT (Reuters) - A first convoy of the military operation that Turkey is carrying out in Syria s Idlib province 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. 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.  The convoy was escorted by fighters from Tahrir al-Sham, an alliance of jihadist groups including the former al Qaeda affiliate previously known as the Nusra Front, Abu Khairo said.   The Turkish army convoy is entering under the protection of Tahrir al-Sham to take positions on the front line with the YPG,  another FSA official in the area said.  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. 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.  Tahrir al-Sham and Euphrates Shield rebels have fought previously and the jihadist alliance has this year battled other insurgents 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 Islamic State from its border, but also at stopping the Kurdish YPG from gaining more sway.  Backed by the United States in its battle against Islamic State, the YPG has seized much of northeastern Syria and was trying to link that territory up 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. 