Turkey's President Recep Tayyip Erdogan is not an Islamist in the extreme sense of the word, but he certainly does like the Islamists a lot. In the heyday of the Islamic State in northern Syria and Iraq, it was Erdogan who kept the Turkish border open so that thousands of foreign fighters and their families could go to join that terrorist proto-state, which was a descendant of al-Qaida.
More recently, he has stationed Turkish troops in Syria's Idlib province, the one remaining rebel-held part of the country, where Hayat Tahrir al-Sham, another offshoot of al-Qaida, rules unchallenged.
Unchallenged, that is, except by Syrian Army troops backed by Russian air power who are gradually winning back control on the province in a slow, grinding offensive that last week captured Idlib's second-biggest city, Maarat an-Numan. So it's no surprise that the Turkish Army in Idlib is now firing directly on Syrian forces.