What happened?
On 26 October, a Russian airstrike in Syria's Idlib province killed at least 78 Turkish backed rebel fighters. They belonged to the moderate Islamist group Faylaq al-Sham, an offshoot of Turkey's Muslim Brotherhood. Idlib is the last rebel-held province in Syria. 

On 28 October, Turkish President Recep Tayyip Erdogan made a statement in the parliament that the Russian airstrike indicated Moscow's reluctance to establish lasting peace in the region. The attack highlights the increasingly strained Russia-Turkey relations; both countries are involved in various proxy wars in the Caucasus, the Middle East and the North Africa region. Further, the airstrike is a violation of the truce between Russia and Turkey implemented on 5 March 2020.

What is the background?
First, the fragile ceasefires. As part of the latest ceasefire, Russia and Turkey conducted joint military exercises along the key M4 highway in Idlib connecting the government-held cities of Aleppo and Latakia. However, over the last few months, joint exercises ceased, and both sides carried out frequent bombings. The recent airstrike, dangerously close to Turkey's border, indicates an escalation of conflict; it is a message to Ankara over various ongoing battles. Previously, Erdogan had also warned that Turkey "reserves the right to retaliate with all its strength against any attack by forces of Syrian President Bashar al-Assad," despite the truce. Prior to this, Russia and Turkey had signed a ceasefire in 2018 and agreed on de-escalation zones in Idlib which were often violated. 

Second, the increasing tensions in the Caucasus and Libya. The airstrike coincides with Moscow's increased contention with Ankara's involvement in the Nagorno-Karabakh region. Though Russia, a close ally of Armenia, has stayed away from involving itself in the conflict, it has accused Turkey of sending Syrian fighters in support of Azerbaijan. Further, the two countries are also engaged in the conflict in Libya. Here, Turkey has deployed Syrian fighters to fight for the UN-recognized Government of National Accord, which is pitted against the Russian-backed Libyan National Army led by General Khalifa Haftar.

What does it mean?
Apart from Erdogan's statement, Turkey has not retaliated so far. If Erdogan decides to retaliate, then Idlib would once again become a regional proxy. Overall, the developments between the two could lead to a cold-war like situation. 

There is another possibility; Turkey might land a strong blow to Russia in either the Caucasus or Libya and use Idlib as a bargaining element. However, since the ceasefire was implemented this year, more than 200,000 displaced Syrians returned home to their towns. Any escalation in Idlib would put Turkey at the risk of an influx of Syrian refugees; currently, Turkey already houses around three to four million Syrian refugees. 

On the other hand, despite conflicting interests, Russia and Turkey have engaged in economic and military agreements. For example, Russia's trade with Turkey stands at $20 billion. In 2019, Turkey purchased the S-400 missile system from Russia despite the risk of sanctions from the West. Therefore, such bilateral cooperation between the two countries results in ambiguity regarding their future course of action.