Turkey risks restrictions on its continued participation in NATO’s mutual air defense system by going ahead with the estimated $2.5 billion purchase of advanced S-400 surface-to-air missiles from Russia, a top NATO general said Wednesday.

“The principle of sovereignty obviously exists in acquisition of defense equipment” by NATO-member Turkey, said Czech Gen. Petr Pavel, chairman of NATO’s Military Committee.

“But the same way that nations are sovereign in making their decision, they are also sovereign in facing the consequences of that decision,” he told reporters at a Defense Writers Group breakfast.

Pavel echoed earlier statements by NATO officials that the S-400 system would not be integrated into the air defense systems of the alliance and suggested Turkey could face other restrictions by going ahead with the purchase, estimated at $2.5 billion.

On Thursday, the U.S. State Department issued a list of more than three dozen off-limits Russian companies and warned businesses and nations worldwide that those doing business with the Russian firms could face U.S. sanctions.

The list of Russian firms includes missile manufacturer Almaz-Antey, maker of the S-400.

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The presence of the S-400 in Turkey would create “challenges for allied assets potentially deployed onto the territory of that country,” Pavel said.

He didn’t define the “allied assets,” but appeared to be referring to the stealthy F-35 Joint Strike Fighter, which several NATO allies have committed to buy.

In pitching the S-400 to Saudi Arabia, Qatar, Turkey and other states, Russia has claimed that the system would be effective against stealth aircraft.

Turkey began talking up its interest in the S-400 system last spring and announced in July that a deal had been made.

In early September, Turkish President Recep Tayyip Erdogan said he had made a down payment, without disclosing the amount, but NATO officials said the deal had yet to be finalized.

Erdogan said he had no choice since NATO and the U.S. had denied him a similar system, and he dismissed the alliance’s objections.

“They went crazy because we made the S-400 agreement. What were we supposed to do, wait for you? We are taking and will take all our measures on the security front,” Erdogan said during a meeting with mayors from his ruling Justice and Development Party (AK Party) in Ankara.

In another sign of Turkey’s increasingly fractious relationship with the U.S. and NATO, its state-run Anadolu news agency published a graphic shortly after the deal was announced touting the ability of the S-400 system to take down U.S. aircraft.

The infographic said the S-400 would be effective against the B-52 Stratofortress, B-1 Lancer, F-15 Eagle, F-16 Fighting Falcon, and the stealthy F-22 Raptor.

According to Russian claims and analysis by Western experts, the S-400 system can fire four intercept missiles with varying ranges.

The system supports the 40N6E-series of missiles with a reported range of 400 kilometers (248.5 miles); the 48N6, 250 km (155.3 miles); the 9M96e2, 120 km (74.6 miles); and the 9m96e, 40 km (24.8 miles).

The missile that most concerns Western defense officials is the short-range 9m96e. The Russians claim the missile flies at nearly 11,500 mph and can knock out high-flying aircraft as well as cruise missiles hugging the ground.

The S-400 system also has acquisition radars that would be effective against stealth aircraft such as the F-35 and F-22, according to the Russian claims.

Despite NATO’s concerns about the S-400 system, Pavel said at the breakfast Wednesday with defense reporters that Turkey is still a valued member of the alliance.

NATO allies are justified in raising “all concerns and potential difficulties” they may have with each other, Pavel said, but “no one challenges the role of Turkey as an important ally at the very difficult crossroads of challenges to the alliance.”