Turkey has dismissed Washington’s threats of imposing sanction on Ankara over its planned buying of Russian S-400 missile defense system, saying the deal is largely done and will not be reversed.

The delivery of Russian S-400 air defense missile systems to Turkey is scheduled to begin in July 2019.

“The ‘I will impose sanctions if you buy’ approach will not affect Turkey. Turkey will not accept this. If we are going to discuss what we can do together in the future, we are in,” said Turkish Foreign Minister Mevlut Cavusoglu who last Friday met in Brussels his newly confirmed US counterpart Mike Pompeo on the sidelines of a NATO meeting.

Cavusoglu’s remarks came after Pompeo raised serious concerns about Ankara’s purchase of the S-400 batteries, and after Washington’s envoy to the NATO military alliance, Kay Bailey Hutchinson, threatened Turkey with “serious consequences” earlier in the week for the Russian deal.

U.S. officials said Pompeo warned Turkey that countries that purchase military hardware from Russia risk running afoul of new sanctions the United States imposed last year on Russia’s military and defense industries.

But Turkish Foreign Minister Mevlut Cavusoglu shortly afterward told Turkish broadcasters that the $2.5 billion purchase of S-400s was signed in December and was “a done deal.”

He said Russia, in fact, was “speeding up the process” of delivering the missile systems at Turkey’s request.

“We have completed the S-400 process. That is a done deal,” he said, telling broadcasters that Turkey would not be deterred by the threat of sanctions.

“The ‘I will impose sanctions if you buy’ approach will not affect Turkey,” he said. “Turkey will not accept this.”

Cavusoglu said Turkey was open to purchasing other weapons from NATO members, however.

“We need more air defense. We can discuss what we can do for further purchases,” he said. “If we are going to discuss what we can do together in the future, we are in.”

Turkey’s plans to purchase weapons from Russia has unnerved some NATO members, which have been building up forces on NATO’s eastern flank because of what they perceive as a growing threat from Russia.

Turkey’s stance risks triggering a backlash in the U.S. Congress, where many legislators are concerned about not only Erdogan’s increasingly friendly stance toward Russia but his jailing of political opponents, journalists, and academics.

The development comes after three US senators introduced a measure in Congress on Thursday to block the transfer of Lockheed Martin’s F-35 Joint Strike Fighter to Turkey, over what they described as Turkish President Recep Tayyip Erdogan’s “path of reckless governance and disregard for the rule of law.”

Turkey plans to buy more than 100 of the F-35s. The bill would not only block the sales but would restrict Ankara’s access to intellectual property and technical data needed to maintain and support the fighters.

The S-400 Triumf (NATO reporting name: SA-21 Growler) is one of the most advanced long-range anti-aircraft missile system that went into service in 2007. It is designed to destroy aircraft, cruise and ballistic missiles, including medium-range ones, and can also be used against ground targets. The S-400 complex is capable of engaging targets at a distance of up to 400 km and at an altitude of up to 60 km. Many components for Russian arms, engines all helicopter and some aircraft engines for example, were produced in Ukraine and now banned for export to Russia.