Turkey reportedly carried out a live-fire test of its Russian-made S-400 defence systems on its Black Sea coast, drawing harsh criticism from U.S. lawmakers on Friday.

A video, taken in the coastal city of Sinop and posted on social media, showed a narrow column of smoke headed high into the sky. In recent days, Turkey had issued notices restricting airspace and waters off the coastal area to allow firing tests.

A U.S. official speaking to Reuters on the condition of anonymity said Turkey had tested the S-400 system on Friday but did not provide details.

Tests of the S-400s, if verified, could stoke tensions between Turkey and the United States, which sharply opposed the Turkish government’s $2.5-billion purchase of the system from Moscow on grounds they compromise NATO’s defence network.

Washington has already thrown Turkey out of a programme to produce and procure fifth generation F-35 stealth fighter jets, and American lawmakers have pushed for sanctions on Turkey required by U.S. law for doing business with Russia’s defence industry – a measure the Trump administration has failed to impose.

U.S. Senator Jim Risch, chairman of the Senate Foreign Relations Committee, called the Friday’s test “unacceptable behaviour” from a NATO ally.

The move damages the alliance and posed a direct threat to the F-35 and other U.S. and NATO allies’ systems, he said in a statement.

“U.S. law requires sanctions against countries that continue to deepen their defence relationship with Russia, and the administration should send a strong signal that Turkey must divest its S-400s,” he said.

Senator Bob Menendez, the ranking Democrat on the Senate Foreign Relations Committee, said President Donald Trump’s affinity for Turkish President Recep Tayyip Erdoğan posed a serious threat to American national security.

“Today’s test by Turkey of the Russian-made S-400 air defence system is a stark reminder that Ankara is not deterred by simple meek pleas coming from the Trump administration, Menendez said in a statement. “Erdoğan only responds to actions, not words.”

He said Turkey must be immediately sanctioned for purchasing and using the system.

Bradley Bowman, senior director of the Center on Military and Political Power (CMPP) at the Foundation for Defense of Democracies (FDD), and military analyst Shane Praiswater, wrote an opinion piece (republished below with permission) on the implications Turkey's live-fire test may have on its relationship with the U.S. and NATO:

Turkey reportedly conducted an expected live-fire test on Friday of its Russian S-400 surface-to-air missile system. The test represents a troubling milestone in the steady deterioration of Ankara’s relationship with Washington and NATO – potentially increasing the chances that Washington will impose sanctions on Turkey under the Countering America’s Adversaries Through Sanctions Act.

Turkey’s live-fire test follows unconfirmed reports that Turkey had used the S-400’s radar to track a Greek F-16. Last year, despite multiple pleas from the United States, Turkey activated the S-400 and conducted initial testing. The live-fire test suggests that Turkey has no intention of stashing the S-400, regardless of objections from Washington or Brussels.

Turkey’s acquisition and activation of the S-400 are troublesome for a number of reasons. First, they constitute a tangible manifestation of Turkey’s drift toward Russia – one of the more significant geo-strategic developments in recent years. This drift is particularly problematic given Moscow’s activities in Europe and the Middle East that threaten core U.S. and NATO interests. Turkey’s drift is also troubling due to the country’s status as a NATO member as well as its strategic location.

Turkey’s employment of the S-400 is also concerning given the system’s ability to practice identifying, tracking, and targeting the F-35. Ankara’s assurances that such information would not find its way to Moscow are not persuasive. The co-location of the S-400 and F-35 would likely enable Moscow to gain valuable intelligence helpful for shooting down F-35s flown by Americans and their allies. For this reason, Washington was right to evict Ankara from the F-35 program last year.

Additionally, the United States and NATO have been transitioning from the “Mode 4” aircraft-identification system to a next-generation encrypted “Mode 5” system. This system allows NATO air defence batteries and aircraft to discern whether an unknown aircraft is a friend or foe. The United States will not allow the S-400 to have Mode 5 capabilities, as doing so would allow Russia to break NATO identification codes and quickly identify aircraft.

However, excluding Turkey’s S-400s from NATO air defence systems would leave Turkey potentially shooting blind in a conflict, when life-and-death decisions are made in seconds. Accordingly, in such a scenario, Turkey would struggle to differentiate NATO from adversary aircraft – potentially resulting in fratricide.

This reality would make Turkey a less capable NATO ally and increase the risk for U.S. and allied pilots operating in or near Turkish airspace.

This could have a direct impact on whether the United States will want to maintain some military forces and systems at the U.S. air base in İncirlik. Regardless, if tensions continue to escalate, Ankara may evict U.S. forces from the base or impose severe restrictions on U.S. operations emanating from the base.

In light of this possibility, one hopes that the Pentagon has updated and detailed plans for the potential relocation of U.S. forces from İncirlik. Greece may provide a potential alternative.

In the meantime, in addition to any potential imposition of sanctions, congressional leaders may want to request a classified briefing from the Pentagon on the implications of this latest S-400 development for U.S. and allied military operations and basing.

After all, an ally should not acquire a cutting-edge air defence system from the leading threat to the alliance. With Erdogan once again brushing aside American concerns, failing to respond assertively could leave Ankara and others with the impression that they can ignore Washington with few consequences.