ISTANBUL - Questions about the future of Turkey's rapprochement with Russia are growing as fallout continues from Monday's killing of at least five Turkish soldiers by Russia-backed Syrian government forces.
The rising Russia-Turkey tension over Syria is now seen as offering an opportunity to the United States to improve strained ties with Turkey.
Turkish President Recep Tayyip Erdogan used a two-day visit to Ukraine to turn up the pressure on Moscow. During the visit, Erdogan condemned Russia's annexation of Ukraine's Crimean peninsula and signed a military deal with Kyiv.
"The situation with Russia, the crisis is accelerating, also with this visit to Ukraine, we've reached a point where the Russian limits will be less and less, with Turkey," said international relations professor Huseyin Bagci of Ankara's Middle East Technical University.
"So the Russians are not happy. The Americans seem to be the winner of the day," added Bagci.
Ankara's deepening relationship with Moscow has caused alarm among Turkey's NATO allies, especially the U.S.
U.S. sanctions are looming against Turkey for Ankara's purchase of a Russian S-400 missile system, an acquisition that violates U.S. law.
But the incident involving the Turkish military personnel in Syria could open the door to a reset with Washington.
"We witnessed before how Erdogan can change his course in foreign policy, it is too early to tell, but we may not have to wait long." said former senior Turkish ambassador Aydin Selcen, who served in Washington.
Despite what happened, Erdogan appeared to step back Tuesday from any rupture with Moscow.
"We do not need to engage in a conflict or a serious contradiction with Russia at this stage," the Turkish president told reporters while returning from Ukraine.
"We cannot overlook these [strategic partnerships with Russia]. That is why we will sit down and discuss everything [with Russia]. Not in anger since it would only bring harm," Erdogan added.
The Turkish president underlined the importance of Turkey's energy relationship with Russia. In January, Russian President Vladimir Putin visited Istanbul to attend an opening ceremony with Erdogan of a new Russian gas pipeline to supply Istanbul.
Turkey depends on Russia for about half of its gas supplies, while a Russian company is building the country's first nuclear power station.
Erdogan also reiterated Tuesday the importance of the purchase of the Russian S-400 missile system, dashing any U.S. hopes that Turkey would not activate the system, which is scheduled for later this year.
Erdogan's relationship with Putin is the driving force behind the country's rapprochement. "This leader's diplomacy is the engine in Turkish-Russian relations," said Selcen.
Ankara's ongoing suspicion of Washington's intentions in the region also remains a powerful impetus to sustaining Turkish-Russian relations.
"There is a break of trust; Turkey is not trusting with the Americans," said Bagci. "In many ways, this lack of trust was the architect of Turkey orienting toward Russia."
Washington's support of the Syrian Democratic Forces in the war against the so-called Islamic State group continues to sour U.S.-Turkish relations, given Ankara designation of the SDF as a terrorist organization linked to a Kurdish insurgency inside Turkey.
"This [support] is perceived as an existential threat to Turkey by Ankara," said Selcen.
President Donald Trump's decision last year, to withdraw American forces supporting the SDF, opened the door to Turkish forces attacking the militia. Ankara was banking on the U.S. withdrawal marking the end to Washington's support of the SDF.
Ambassador James Jeffrey is the U.S. special representative for Syria engagement and special envoy to the Global Coalition to Defeat ISIS. This week, he reaffirmed Washington's ongoing support for the SDF.
"We had a setback temporarily in Syria back in October with the Turkish incursion, but we're back doing full operations with our local partner, the Syrian Democratic Forces," Jeffrey said Thursday during a State Department telephone briefing.
Washington's ongoing support of the SDF continues to fuel Ankara fears that ultimately an independent Kurdish state could be created.
"What's important regarding Syria for Turkey and the Russian Federation is that they keep maintaining the territorial integrity of Syria — while we are not on the same page with the United States," said former Turkish ambassador Mithat Rende.
"We are quite disappointed [with Washington]," he added, "Not only the government but the Turkish people. Because they disregard the vital interests of Turkey, we are against establishing mini-states."
Monday's death of the Turkish soldiers is seen as a warning of how little leverage Ankara has in its relationship with Moscow.
"Right now, Putin knows, we [Turkey] have no intention to go back to the United States. So he has no incentive, no intention to give us even some breadcrumbs, concessions," said analyst Atilla Yesilada of Global Source Partners. "Because he knows he will get whatever he wants from Turkey. Now we say no to whatever the U.S. says and yes to Russia."
Until the trust deficit between Ankara and Washington is bridged, efforts to improve ties are predicted to remain tense. Analysts point out Washington still has failed to dispel suspicions of its involvement in a failed military 2016 coup to overthrow Erdogan. Putin was among the first to offer support to Turkey on that violent night.
Analysts say Erdogan also is aware of what a dangerous adversary Putin can be.
"Erdogan will be careful at the end of the day not to anger Putin because we know when Putin gets angry, we have troubles," said Bagci.