Turkish forces using artillery and jets hit Syrian government military targets across Syria's Idlib province Monday. Turkish President Recep Tayyip Erdogan said the offensive was in retaliation for a deadly attack by Damascus on Turkish soldiers.
"Those who test Turkey's determination regarding Syria's Idlib with such treacherous attacks will realize their mistake," Erdogan told reporters before departing for a visit to Ukraine.
"It is not possible for us to remain silent when our soldiers are being martyred," he added.
Erdogan said 46 Syrian targets had been identified and were being hit by heavy artillery and F-16 fighter bombers. The Turkish president said "initial reports" confirmed between 30 and 35 Syrian regime casualties."
The assault, Erdogan said, was in response to Syrian government artillery killing at least five Turkish soldiers and injuring others, some seriously.
The five Turkish soldiers were part of a group deployed to enforce an agreement with Russia, to create a "de-escalation zone" in Idlib between Syrian rebel and government forces.
Idlib is Syria's last rebel enclave and home to more than 3 million people.
Tensions between Ankara and Damascus have been escalating with Syrian government forces launching a major assault on Idlib, which threatens to cause a new major refugee exodus into Turkey. Turkey currently hosts more than three-and-a-half million Syrians.
Erdogan has repeatedly called on Damascus to end its Idlib assault, warning he would not stand by. In the last few days, Ankara has sent reinforcements into Idlib, including tanks and armor.
With Ankara a strong backer of the rebels, analysts warn of the risk of military confrontation with Damascus.
Warning to Moscow
The escalating violence also poses a significant challenge for Turkish-Russian relations. Moscow, while backing Damascus, has developed close ties with Ankara, but the balancing act is facing the most significant test.
Erdogan Monday sent a warning to Moscow. "More importantly, if we do not reach the results desired [in Idlib], then I will speak with my [Russian] counterpart and convey to him the critical nature of the matter," the president said.
In the last few years, there has been Russian-Turkish rapprochement widely seen to be built on the personal chemistry between Erdogan and Russian President Vladimir Putin.
Despite different regional objectives, Erdogan and Putin have successfully cooperated; however, agreements on Syria aimed at ending the fighting and ultimately achieving a long-term peace, appear under threat, with the escalating violence in Idlib.
"Definitely relations will be damaged, but they won't break down," said international relations professor Huseyin Bagci of Ankara's Middle East Technical University.
Bagci, however, says the cause of the current tensions and violence remains.
"The Syrians want to get rid of the radical groups in Idlib, and Turkey is using these groups as an instrument, for the presence of Turkey in northern Syria to give it leverage over Damascus," Bagci added.
The Syrian government's Idlib offensive is backed by Russian firepower. Moscow blames Ankara for the fighting in Idlib, accusing it of failing to disarm and remove "terrorist elements," as part of a de-escalation agreement last year.
The Russian Defense Ministry also said the killing of the Turkish soldiers Monday was Ankara's fault.
"Turkish troops were changing locations at night in the Idlib de-escalation zone without informing the Russian side," the ministry said in a statement.
Omer Celik, a spokesman for Turkey's ruling AKP, dismissed Moscow's claims and appeared to ratchet up tensions further.
"The [Syrian] regime is from now on a target for us in the region after this attack," Celik said.
"We expect Russia not to shield the regime or protect them because, after the clear attack on our armed forces, regime forces around our posts are targets," he added.
Moscow showing restraint
Moscow has so far refrained from directly criticizing Turkey's Syrian operation. Both Ankara and Moscow have confirmed military officials are in communication.
Erdogan said his spy chief, Hakan Fidan, would also hold talks with Russian officials.
Analysts suggest Moscow will likely want to defuse tensions with Ankara, aware of the concern with Turkey's NATO allies, over the Turkish-Russian rapprochement.
But the killing of the soldiers in Syria is likely to fuel growing questions in Turkey over the value of cooperating with Moscow in Syria.
"The big question is why we side with Putin - what has this relationship done for Turkey in Syria or anywhere else," said analyst Atilla Yesilada of Global Source Partners, an economic and security research group based in New York.
"Putin just doesn't keep his promises, but we seem to be beholden to him for reasons which are beyond me. I don't see any strategic reasons for sticking with this Russian alliance, which doesn't deliver us much. "
Last month, Erdogan warned that unless Russia started honoring its agreements on Syria, Ankara would go its own way.
Some analysts question whether Erdogan is ready to sacrifice his relationship with Moscow, which he described as "strategic." But with Turkey facing the threat of a new Syrian refugee exodus from Idlib, and Moscow's apparent reluctance to rein in Damascus, the Turkish president's options are becoming increasingly limited.