MOSCOW, July 24. /TASS/. Russia has launched an operation to deliver the 2nd regiment set of S-400 surface-to-air missile systems to China by sea, a source in military and diplomatic circles told TASS on Wednesday.

"A transport vessel with the first batch of hardware from the second S-400 regiment set for China has taken to the sea from the port of Ust-Luga on the Baltic coast. Therefore, like in the case with Turkey, the deliveries of the systems have started several months ahead of the term stipulated in the contract," the source said.

The delivery of the entire S-400 regiment set to China envisages "involving no less than three vessels" that will take to the sea one by one "within short time intervals," the source added.

Russia’s Federal Service for Military and Technical Cooperation declined to comment for TASS on the information provided by the source.

China became the first foreign buyer of Russia’s most advanced S-400 ‘Triumf’ surface-to-air missile systems. Russia signed a contract with China on the delivery of two regiment sets of S-400 air defense missile systems in 2014.

The first regiment set of S-400 anti-aircraft missile systems was delivered to China in the spring of 2018. The Chinese military successfully test-fired the missile launchers from the first S-400 regiment set, striking an aerodynamic and a ballistic target at its firing ranges.