The US State Department said that Washington has expressed to high levels in the Turkish government that it does not accept Ankara's possession of Russian weapons systems such as the S400, and has warned of "potentially serious consequences" for its security relationship with Turkey if it operates this system.
In a statement today, Friday, ministry spokeswoman Morgan Ortagus said that Washington had seen news reports that Turkey was experimenting with the S-400 system.
"If this is confirmed, we will condemn in the strongest terms the test of launching a missile from the S-400 system, as it is inconsistent with Turkey's responsibilities as a member of NATO and as a strategic partner of the United States," she added.
Earlier, Reuters said it had obtained a local video recording showing the launch of a missile - on Friday - from the coast of Turkey on the Black Sea.
The video, which was filmed in the coastal city of Sinop, showed a thin column of smoke rising towards the sky.
The agency noted that Turkey has issued notifications in recent days to impose restrictions on traffic in airspace and water in this coastal region, to conduct military tests.
Reuters quoted military analyst Turan Oguz as saying that the initial assessment of the color, density, angle and trajectory of the smoke in the video matched the S-400 missiles.
Neither denial nor affirmation
For its part, the Turkish Ministry of Defense said that it will not deny or confirm that tests of launching missiles from the S-400 system have been conducted.
Last year, the Turkish army conducted radar tests for the Russian system, which is one of the most advanced defenses in the world, and can monitor and track incoming aircraft on a medium and long range.
Turkey signed the S-400 deal with Russia in 2017, and deliveries of the first 4 missile batteries worth $ 2.5 billion began in July 2019.
Two US senators called again for President Donald Trump's administration to impose sanctions on Turkey, after news of the planned experiments circulated in recent days.