China became the first foreign buyer of Russia's advanced S-400 air-defense system in late 2014.

The components of Beijing's first S-400 regiment arrived in China this month.

The system could give the Chinese military broader coverage of the South China Sea, where it has made a number of disputed territorial and maritime claims.

The first regimental set of the Russian-made advanced air-defense system known as the S-400 has arrived in China, a military-diplomatic source told Russia's official news agency Tass this week.

China became the first foreign buyer of the S-400 when it signed a contract in late 2014, and the first two ships carrying S-400 components from Russia arrived in China at the beginning of April.

According to the Tass report, cited by The Diplomat, a third and final ship carrying support equipment arrived this month.

"The ship has brought the equipment not damaged during a December storm in the English Channel and the damaged equipment after repairs," the source said, referring to what a Russian military spokeswoman described as secondary components that were returned to Russia after the storm.

The arrival of all three ships brings a full regimental set of the S-400 system to China, including command centers, launchers, guided missiles, and power-supply equipment. Russian personnel are to start handing the equipment over to China at the end of May — a process expected to take two months, according to Tass.

An S-400 regiment consists of two battalions, and each battalion, also referred to as a division, has two batteries, according to The Diplomat. A standard battery has four transporter erector launchers — each with four launch tubes — as well as fire-control radar systems and a command module.

Some reports indicate that China purchased four to six S-400 regimental sets, though the Tass report said Beijing is only getting two.

China is only one of several foreign buyers. Turkey, India, and Saudi Arabia have all reportedly bought the S-400 or are in talks to do so.

While the S-400 has not been used in combat conditions, it has been heralded as one of the best air-defense systems in the world. The deployment of a second division to Crimea earlier this year worried US military officials, who said it could give Russia more coverage of the Black Sea and was a sign of Moscow's willingness to use force.

In addition to having improved radar, the S-400 can reportedly fire several new and upgraded missiles with ranges up to 250 miles.

Russian S-400 Triumph/SA-21 Growler surface-to-air-defense systems in the Victory Day parade at Red Square in Moscow, May 9, 2015. Reuters

China reportedly has 15 divisions of the S-400's predecessor, the S-300, stationed along the coast of Fujian, a province in the country's southeast overlooking northern Taiwan.

Depending on which missiles China's S-400s are equipped with, batteries in Fujian could reportedly cover all of Taiwan, while batteries placed in northern Shandong province could reach the Diaoyu/Senkaku Islands, over which Japan and China dispute control.

While its eventual armaments are not clear, the S-400 arrives in China at a time of increased tension in the region.

China has been more hostile toward Taiwan, which claims independence but China views as its territory, since Taiwan's 2016 election of President Tsai Ing-wen, who has said she wants peace but Beijing suspects wants formal independence.

China has stepped up its military exercises around Taiwan over the past year, including several in April, which were followed by two US Air Force B-52H Stratofortress bombers patrolling through the area — reportedly flying within 155 miles of the southern Chinese coast.