ANKARA, July 1 (Xinhua) -- Moscow and Ankara have reportedly agreed upon a deal for the supply of S-400 long-range surface-to-air missile systems to Turkey, which experts say should not alarm NATO.

No other NATO country has bought the advanced air defense systems before, believed to be incompatible with the alliance's systems.

The deal was confirmed on Thursday by Russia's presidential advisor Vladimir Kozhin. "The contract has been agreed and everything is understandable there but the issue of a loan, funds, has not been settled yet," he said, quoted by the Russian press.

Recently, top Turkish authorities have voiced an official interest in purchasing advanced S-400 air and missile defense systems from Russia.

Turkey's efforts to enhance its defensive strategic military capabilities is not new. For some years now it has sought to have a long-range missile defense system of its own, as it is currently relying on NATO-deployed ballistic missile.

In 2013, Ankara awarded a tender to a Chinese company for missile defense systems procurement, which drew a sharp reaction from its NATO allies and the 3.4 billion U.S. dollars deal had to be scrapped. Other bidders at that time were the United States with Patriot systems, and the French-Italian consortium with the SAMP/T Aster-30 Block-1 variant. It was known that Russia showed interest in the tender, but it was not shortlisted.

This time, amid the tense Turkish-European relations and the ongoing frictions with major NATO ally, the United States on Syria, where the U.S. administration is supplying military equipment to the Syrian Kurds that Ankara considers as terrorists, this major non-NATO arms deal with Moscow could also cause some problems.

"I don't see how this deal, if it's finalized, should worry NATO. Variant of this missile system is actually deployed in other NATO countries such as Greece and Bulgaria, just to mention a few," said to Xinhua Professor Togrul Ismayil from the Ankara-based University of Economics and Technology.

This expert on Russia explained that this deal is also a "positive move" for NATO who has failed to supply permanently this kind of system to Turkey located in a strategic geography plagued with wars and internal conflicts.

In the past, several Patriot missile battery from the United States, Germany and the Netherlands were deployed on Turkish soil near the Syrian border but they were subsequently pulled after delicate negotiations with these countries, angering the Ankara government.

According to experts, the decision by NATO allies to pull their missiles legitimize Turkey's necessity to try to establish its own system in order to reduce its foreign dependency.

"Turkey's strategic defense needs can not be left to other NATO allies tantrums. Turkey is only doing something natural which is to boost its air and defense missile," pointed out Professor Ismayil.

Technically, there is no rule within the NATO treaty that would prohibit member states from procuring Russian arms, and there are allied nations that currently have them, although Russian strategic weapons in NATO-member nations' arsenals seem problematic for allied coherence, according to some analysts.

"There is a big problem with the integration of this Russian system to the NATO one," explained to Xinhua Ozgur Eksi, an Ankara-bases defense analyst with C4 Defense.

He indicated that Turkey might use the S-400 for national purposes without incorporating it to the NATO system. "She has all the right to do so as its neighbour Iran is currently much more advance in this field."

But, he added, integration and compatibility with NATO is another thing.

"Let us think in a theoretical way what will happen if this equipment is integrated in the NATO system: It will be if Russia will step into your bedroom," said Eksi.

If successful, the S-400 would be the largest bilateral defense program between Turkey and Russia. Their bilateral relations briefly collapsed in 2015 following the downing of a Russian fighter jet but Ankara and Moscow succeeded to repair ties since then.

The S-400 system is Russia's next generation air defense system. It can carry three types of missiles capable of destroying targets including ballistic and cruise missiles.

Commercial and political issues need still be settled before a final contract can be inked. Talks on financial details are ongoing and will not be disclosed, according to government sources.

"Turkey's ultimate goal is to produce its own air defense system in time. We are working on that too," said to Xinhua a source who preferred to remain anonymous.