Vietnam is moving its new Israeli-made rockets to the South China Sea

Vietnam has brought mobile rocket launchers from its mainland to islands in the South China Sea, which is likely to increase tensions with China, according to Western officials.

These rocket launchers are now close enough to hit targets on Chinese-controlled islands in the disputed area, according to the military officers and diplomats who spoke to Reuters.

Control of islands in the South China Sea has long been a point of contention between China and Vietnam, while Taiwan, Malaysia, the Philippines and Brunei also have made claims to portions of this area.

On Wednesday, China's foreign ministry told Reuters that it has "indisputable sovereignty over the Spratly islands and nearby waters" and "resolutely opposes the relevant country illegally occupying parts of China's Spratly islands and reefs."

In July, a case brought to an international court by the Philippines found that China lacks any legal basis to its claims to a large chunk of the area.

Vietnam's fortification of its islands over the last few months is in response to a Chinese buildup of various military installations on the islands it controls, according to Carl Thayer, an official at the Australian Defence Force Academy specializing in Vietnam's military.

"China's runways and military installations in the Spratlys are a direct challenge to Vietnam, particularly in their southern waters and skies, and they are showing they are prepared to respond to that threat."

Thayer says that China, however, is unlikely to perceive the rocket transfer as a defensive move, meaning increased militarization of the area may be imminent.

The rocket launchers Vietnam has moved into the islands are part of an elaborate artillery system purchased from Israel, according to military officials.

They are currently unarmed and hidden from surveillance, Reuters reported, but may be ready to fire within the next couple days.

Follow Davide Mastracci on Twitter: @DavideMastracci