Russian President Vladimir Putin is visiting Istanbul Wednesday, where he will meet his Turkish counterpart Recep Tayyip Erdogan. Bilateral relations have dramatically improved much to Ankara's western allies' concern, but escalating regional differences threaten to sour those bilateral ties.
Putin is officially going to Istanbul to inaugurate a key new gas pipeline between Russia and Turkey.
The Turk Stream pipeline will supply Istanbul with Russian gas.
"This ceremony tomorrow will mark a new beginning of Russian gas supply increasing to Turkey and European markets," says Mehmet Ogutcu, head of the London Energy Club.
Turkey, as a market and transit country for Russian energy, is widely seen as the bedrock of deepening bilateral ties.
"Cooperation in the field of energy is high on the agenda of Turkish Russian agenda," said former Turkish ambassador Mithat Rende, who is now an energy expert. "It's important because we are not oil-rich or gas-rich, and we are quite dependent on gas and oil."
While energy cooperation continues to deepen, there are rising bilateral tensions.
Turkey is facing a new Syrian refugee crisis, because of a Russian-backed offensive by Damascus forces, against the rebels' last enclave in the Idlib province.
"We are seeing signs of friction over Syria, the Idlib situation is quite worrisome, and Russia is bombing there, and there is a huge exodus of people fleeing toward the Turkish border," said Ogutcu. "If you have another 250,000 refugees crashing the border and coming, that will have serious domestic implications for Erdogan, as well."
With Turkey already hosting more than 3.5 million Syrian refugees, there is growing Turkish public discontent. A series of recent local election setbacks suffered by Erdogan's ruling AKP Party is widely blamed on a toxic combination of a slowing economy and anger over the ongoing presence of refugees.
More than 3 million people are trapped in Idlib, and analysts suggest it will top the agenda of Erdogan's talks with Putin.
"Idlib is the biggest issue," concurs Huseyin Bagci of Ankara's Middle East Technical University "Idlib will remain an unresolved conflict between Russia and Turkey. Idlib is a big threat to Turkey; there is a real fear of a huge wave of refugees."
The Libyan civil war is another potential flashpoint. Erdogan is sending soldiers in support of the Tripoli-based government, which is fighting forces of General Khalifa Haftar backed by Russian mercenaries linked to the Kremlin.
"It looks like General Haftar gets a very strong push by forces supported by Putin. So it seems the regime supported by Turkey is losing," said Ogutcu.
"So Erdogan will be looking for common ground so that Turkey, Russia, Algeria, Tunisia can work together. But I am not sure Putin is ready for that. It's going to be a hard bargain."
The widely reported personal chemistry between Erdogan and Putin has overcome previous policy differences. Experts say that chemistry likely will be called upon again in the latest escalating rivalries.
"The two leaders, they get together very often. They seem to get along very well," said Rende. "So it's important to try to maintain a dialogue aimed at narrowing the differences and trying to find a common denominator in the interests of the people of the region and the interests of Syria as a whole."
The dynamics of the Putin-Erdogan relationship are increasingly surrounded in a veil of secrecy.
"There is good personal chemistry between Erdogan and Putin. But we don't really know what they are discussing. It's not a normal state-to-state relationship. It's more a personal relationship at the highest level," said Ogutcu.
"When they meet, it's usually only with their closest aides present or just a translator," he added. "I don't think the establishment, at least on the Turkish side, is involved in what is discussed between the two leaders. But there is an imbalance in favor of Russia in relations. The relationship is not of equals. It's not balanced; it cannot be long-lived, and both sides have to understand that."
Analysts point out, at least in the short term, there appear strong incentives for both Ankara and Moscow side to continue working together. However, escalating tensions over conflicting regional interests are likely to continue to challenge bilateral relations.
Istanbul is in the grip of a winter storm that kept a visiting Russian cruiser at sea. For Erdogan and Putin, they will be hoping such weather is not a harbinger for their talks Wednesday.
