© REUTERS/Vitaly NevarFILE PHOTO: A new S-400 "Triumph" surface-to-air missile system is shown after its stationing at a military base outside the town of Gvardeysk near Kaliningrad, Russia, March 11, 2019.
The video, taken in the coastal city of Sinop, showed a narrow column of smoke headed high into the blue sky. In recent days Turkey had issued notices restricting air space and waters off the coastal area to allow firing tests.
Tests of the S-400s, if verified, could stoke tensions between Turkey and the United States, which sharply opposed Ankara's purchase of the weapons from Moscow on grounds they compromise shared NATO defence systems.
State Department spokeswoman Morgan Ortagus said the United States has expressed to the most senior levels of the Turkish government that the acquisition of Russian military systems such as the S-400 is unacceptable, adding that Washington has been clear on its expectation that the system should not be operationalized.
"We have also been clear on the potential serious consequences for our security relationship if Turkey activates the system," Ortagus said.
"If confirmed, we would condemn in the strongest terms the S-400 test missile launch as incompatible with Turkey's responsibilities as a NATO Ally and strategic partner of the United States," she added.
Turkey's defence ministry said it would neither deny nor confirm missile tests.
Washington reacted last year by suspending Turkey from its F-35 jet programme and has threatened sanctions.
Defence analyst Turan Oguz said a preliminary assessment of the colour, intensity, angle and route of the smoke in the video coincided with S-400 missiles. The angle of the column suggested the target "must not be too high," he added.
Last year the military conducted radar tests of the surface-to-air defences, which is among the world's most advanced and can spot and track incoming aircraft at medium and long ranges.
Turkey signed the S-400 deal with Russia in 2017. Deliveries of the first four missile batteries, worth $2.5 billion, began in July last year.
Last week - after reports of the planned tests circulated - two U.S. senators called again for President Donald Trump's administration to impose sanctions on Turkey.
Lying sacks of shit, all of them. 298 people died for no reason, so they can all lie about it. Meaning, OUR government and those of Holland, Germany, Britain, and every EU country. Sons of bitches, one and all.