An exclusive Reuters report reveals that Vietnam has “discreetly fortified several of its islands in the disputed South China Sea with new mobile rocket launchers capable of striking China’s runways and military installations across the vital trade route.”

According to intelligence reports, Vietnam quietly shipped the rocket launchers from the mainland to five bases in the Spratly Island chain during the last few months, keeping them hidden from aerial surveillance. This means the launchers are not currently operational, but could be armed within days.

“Foreign officials and military analysts believe the launchers form part of Vietnam’s state-of-art EXTRA rocket artillery system recently acquired from Israel,” Reuters reports.

The system has an effective range of up to 93 miles, and can hit both ships and ground targets with the aid of targeting drones … putting China’s new military-grade runways and reinforced hangars on Subi, Fiery Cross, and Mischief Reef within range.

Both the Vietnamese Foreign and Defense ministries disputed the report, with the latter insisting that Vietnam could move weapons into the disputed region of the South China Sea “within our legitimate right to self-defense.”

China’s Foreign Ministry faxed Reuters a fiery statement declaring 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 and on these illegally occupied Spratly islands and reefs belonging to China carrying out illegal construction and military deployments.”

Reuters’ sources seem quite adamant that those rocket launchers are in play, with military analysts calling it “the most significant defensive move Vietnam has made on its holdings in the South China Sea in decades.”

These analysts suggested Vietnam began moving the rockets because they were nervous about how China would handle a loss at the international court of arbitration in The Hague, a case against the Philippines, which they did indeed lose.

Also, Vietnamese military strategists are reportedly nervous about the force China could project from the military installations it has been building on the disputed islands. China, in turn, will be severely displeased with the notion that Vietnam can hit its airfields with salvos from small, highly mobile rocket launchers.

Reuters notes there is also some bitter history between Vietnam and China over the Spratly Islands, after the Chinese defeated Vietnam’s navy to take some of the territory in 1988, killing several dozen Vietnamese soldiers.

The Financial Times is one of many international media outlets to say Vietnam did not respond to its request for comment on the Reuters report. FT mentions recent cyber attacks against Vietnam, which appear to have been carried out by China-affiliated or China-sympathetic hackers, as signs of rising tensions between the two nations.