Turkey's Foreign Minister Mevlüt Çavusoglu

NATO has positively approached Turkey's proposal to form a joint working group to ease concerns over its purchase of Russian S-400 missile systems, Foreign Minister Mevlüt Çavuşoğlu said Friday.

“We still haven't heard back from the US but NATO has approached our proposal positively," Daily Sabah reported quoting Çavuşoğlu as saying.

Washington has for long opposed Ankara’s decision of purchasing Moscow’s S-400 systems on grounds that it would be compromising the security of the F-35 jets that Ankara wanted to buy.

"We never found these claims credible. There are S-400s in Syria and F-35 jets have flown over them repeatedly. If those claims are true, those missile systems would have already gathered enough information about the aircraft," he said.

“So Turkey offered the US to establish a working group with them, to ease concerns over security and to determine whether the S-400s posed a threat to the F-35 fighters,” he explained.

The minister goes on to say that Ankara does understand NATO’s concerns but adds that Turkey urgently needed to procure air defense systems.

Turkey was initially denied the US-made Patriot defense systems that forced it look for other sellers. Moreover, Russia offered a better deal that includes technology transfers, the report added.

The US then began persuading Turkey to procure NATO-compatible Raytheon’s Patriot systems, but Turkey has turned down the offer.

In the first week of April, the US reportedly halted delivery of parts and services related to the stealth F-35 fighter aircraft to Turkey. It marked the first concrete US step to block delivery of the jet to the NATO ally in light of Ankara's planned purchase of the Russian missile defense system.

The US also threatened to impose sanctions against Turkey and also reportedly planned to drop Ankara from F-35 program.

But, a decision to drop Turkey from the F-35 program will have broad repercussions. Turkey has invested $1.25 billion in the F-35 program. Ankara also helps manufacture 6-7 percent of parts for the aircraft, including components of the landing gear, cockpit displays and aircraft engines.

During last week, Russia's Presidential spokesperson said Turkey can produce components for the S-400 missile defense systems.