Turkish Foreign Minister Mevlut Cavusoglu said on Thursday that Russia's S-400 air defense system was compatible with NATO, which needed to set up a working group to study it. 

"The claim is that the S-400 and F-35s are incompatible. That's the claim. Here is our proposal, let's have a working group and NATO can chair this and let's let experts make the assessment and come back to us," he said. 

"We believe the S-400 and F-35 are compatible," Cavusoglu said during a panel discussion at the annual meeting of the World Economic Forum in Davos. "It does not pose any threats to the NATO system or to NATO allies." 

NATO chief Jens Stoltenberg said the bloc and its key member have failed to find common ground over Russia's delivery of the S-400 system to Ankara. 

The delivery of the system, in a deal strongly backed by Russian President Vladimir Putin and his Turkish counterpart Recep Tayyip Erdogan, has deeply troubled Ankara's NATO allies and raised the risk of U.S. sanctions.

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"So far it has not been possible to reach an agreement on that," Stoltenberg said at the panel discussion alongside Cavusoglu.   

"We will try to do whatever we can to find a way to solve these issues, as this is one of the issues that is causing problems within the alliance – there is no way to deny that," Stoltenberg added.  

Cavusoglu had argued in front of Stoltenberg that Turkey had no choice but to buy the S-400 due to a dwindling presence of NATO air systems on its volatile borders, including the one with Syria. 

On the other hand, the Turkish foreign minister called for the enlargement of NATO and the addition of Georgia to the organization. 

"I don't understand why we have not invited Georgia or we haven't activated the action plan for Georgia to become a member," he said. 

"We are criticized for having relatively better relations with Russia as a neighbor, but our Western friends are not agreeing to invite Georgia because they don't want to provoke Russia. But Georgia needs us and we need an ally like Georgia. So we need enlargement and Georgia should be made a member," Cavusoglu stressed.

(With input from Reuters, AFP)