The seizure by the Syrian government forces of Khan Sheikhun in the northwestern province of Idlib may change the agenda of Turkey-Russia relations. An agreement was signed on Sept. 17 last year in Sochi to postpone an Assad regime offensive in exchange for establishing a 15km-20 km demilitarized zone in the province. All radical terrorist groups were to be cleared from the zone by Oct. 15, together with their heavy weapons. Turkey promised to use its leverage to disarm them. It fulfilled this promise with some, but failed with many others. However, it was a common knowledge that, after having defeated the opposition in most of the country, Assad regime forces would eventually turn to Idlib. When they started to make inroads to the center of Khan Sheikhun, Ankara thought the security of its observation post in Morek was threatened, and decided to send reinforcements. The Syrian government claimed that this reinforcement was aimed to help the defeated terrorists of Hayat Tahrir Al-Sham (HTS) in Khan Sheikhun. It attacked the convoy last week and killed three people, including Hussein Kassem, the commander of the Turkey-supported Faylaq Al-Sham militia. Turkish media criticized Russia for not doing enough to prevent the Syrian air force from attacking the convoy. In fact, Moscow not only failed to halt the attack, it also actively supported it. Russian President Vladimir Putin observed: “Before the Sochi agreement on Idlib was signed, about 50 percent of that territory was under terrorist control, and now that number is 90 percent. There were also numerous attempts to attack our air base in Khmeimim from the Idlib zone, so we support the Syrian army’s efforts to carry out local operations to neutralize these terrorist threats.” Russia’s discontent with Turkey’s attitude is hardly concealed in this statement. Turkey was disillusioned by this, because its perception of the Sochi agreement’s ultimate objective was probably different from that of Russia. For Russia, the background of the Sochi agreement was as follows: When the Syrian army was about to launch a military operation in Idlib, Turkey asked Russia to persuade the Syrian government to postpone it, hoping that it may persuade some of the moderate opposition groups to lay down their arms. Turkey woke up to the reality after its convoy was attacked. Yasar Yakis Moscow intervened for postponement, because it thought Turkey’s worries about a possible massive refugee wave toward its borders were justified. Second, if Turkey could persuade some of armed factions to lay arms, this was going to become an added value for stability. On the other hand, Russia considered some of the HTS-linked factions to be legitimate targets, while Turkey did not. Therefore, Russia did not want to continue to pressure Damascus into further postponing the military operation in Idlib. This was the gist of the Sochi memorandum according to Russia. Turkey’s reading of the same agreement seems to be slightly different: Ankara thought that Syria’s postponement of the military operation in Idlib was going to last longer. Therefore, it perceived the agreement as a basis for Turkey’s extended stay in Idlib. Turkey woke up to the reality after its convoy was attacked. Another noteworthy coincidence is that this blow came weeks after Turkey rebuffed strong US pressure because of its purchase of the Russian-made S-400 air defense system — in other words, at a point where Turkish-American relations had hit a low point. Another subject of disagreement with the US is the question of a safe zone in northeast Syria. A concrete step has been taken there, but with uncertain prospects. Depending on how this affair will progress, Ankara may have to re-assess its cooperation with Russia in Idlib. The process will probably continue in light of the military initiatives that the Syrian government will take — with or without the tacit approval of Moscow — and Turkey’s response to them. This question was raised by Erdogan last week during his telephone conversation with Putin. The Kremlin said: “The two sides agreed to eliminate the threat of terror and intensify their common efforts to implement the Sochi memorandum.” This language suggests that both sides maintained their position. The reference to the implementation of the Sochi agreement may be a message to Turkey’s failing in fulfilling its promise to disarm the rebel opposition. Erdogan is due to go to Russia this week. More detailed talks will take place on the security of the Turkish observation posts in Idlib, but if the Syrian regime eliminates the rebel presence in Idlib, the Turkish observation posts that were supposed to observe the de-confliction may lose their relevance.