ANKARA, April 7 (Xinhua) -- Turkish President Recep Tayyip Erdogan will hold talks with his Russian counterpart Vladimir Putin on Monday in Russia amid a controversial missile deal between the two sides which threatens to further deteriorate Turkey-U.S. ties.
Erdogan and Putin have already met more than a dozen times and had several phone conversations in recent months, making significant progress in strengthening their bilateral ties. This time, the two leaders will attend the High Level Russian Turkish Cooperation Council meeting in Moscow.
The new meeting signals deepening ties between the historical rivals just as Turkey's links to its traditional NATO ally the United States grow bitter over Ankara's planned and determined purchase-deployment of state-of-the-art Russian S-400 missiles.
Before the Erdogan-Putin summit, their foreign ministers Mevlut Cavusoglu and Sergey Lavrov met on March 29 in Turkey's southern Mediterranean resort city of Antalya.
They dwelled on a variety of issues, such as Syria, where the two countries are in a strenuous cooperation in the rebel-held northern Idlib province, and passport-free travel for Russian citizens who flock to Antalya every year for holidays.
Ankara and Moscow have had a tough time coordinating their efforts controlling and disarming al-Qaida-linked jihadists in Idlib over the past few months in line with the Astana process that they are implementing with Iran.
But as a new and concrete development, Turkish and Russian forces conducted independent but coordinated patrols in late March in northern Syrian region of Tal Rifaat.
"There is and probably will be problems there (Idlib) but Turkey and Russia are determined to cooperate in this field. They are going in line with their engagements," said Russian affairs expert Togrul Ismayil from Kahramanmaras Unversity.
However, Turkey's main challenges in foreign policy in the near future is difficult dilemma over its choice of Russian missiles despite U.S. and NATO warnings amid concerns that the Russians could use their system to spy on the F-35 aircrafts.
After months of hedging, the Pentagon announced on April 1 that it has suspended deliveries and activities related to the stand-up of Turkey's F-35 operational capability and warned if Turkey takes the delivery of the S-400, its "continued participation in the F-35 program is at risk."
Washington insists that the S-400 is incompatible with NATO capability and is not interoperable. It has also threatened to impose new sanctions on Ankara, despite the fact that the two countries have been NATO allies since 1952.
On Wednesday, U.S. Vice President Mike Pence delivered a new and staunch warning to Turkey on Twitter.
The reply to the American warning came on Friday from Erdogan himself who repeated that his country will not turn back from its major arms deal with Russia.
"The S-400 deal is a done deal," he told reporters in Istanbul, indicating that the United States failed to give a deal on their Patriot air defense system comparable to the one, offered by Russia on its S-400s, state-run Anadolu agency reported.
U.S. officials reportedly still hope that President Erdogan, who had just suffered a setback in local elections, would have second thoughts about bucking the NATO alliance by buying advanced Russian anti-aircraft missiles.
"The shipment (of Russian S-400 missiles) is to begin in July," added the Turkish leader.
Some Turkish experts argue that the S-400 can work outside the NATO realm without compromising its capabilities.
"It's incomprehensible to understand why the U.S. is throwing a tantrum on the S-400 issue. Turkey has insistently said that it will only use it for national defense requirements," said Ismayil, recalling that in the past Ankara had wanted to acquire Patriot missiles but the request was rebuked by Washington.
Turkey is not only a customer for the Lockheed Martin F-35, but also one of the eight international partner nations that build key components for the jet, including parts of fuselage and cockpit displays.
Ismayil expressed concerns that Turkey could drop the deal. He said, however, it "would hurt Turkey's credibility" and the nation would still have to pay a hefty fine to Moscow.
But even Ankara changes its mind in acquiring Russian missiles, its cooperation in many fields, such as conventional and nuclear energy, commerce, culture and tourism with Moscow are expected to be deepened in the future.