Foreign Ministry deputy spokesman Doan Khac Viet said the horticultural activity was a violation of Vietnam’s sovereignty and international law.

"All activities on the Hoang Sa and Truong Sa (Spratly) Islands without Vietnam’s permission are violations of Vietnam’s sovereignty and international law," Viet said at a press meet Thursday.

He was responding to queries about a Global Times report on May 19 that said the Chinese navy had used new agricultural technologies to harvest 750 kg of vegetables on what it calls the Xisha Islands.

The Chinese media outlet also made a dubious claim that the harvesting vegetables on the Paracel Islands proves that the geographical feature is an island, thus cementing China’s claims in the area.

It quoted Chen Xiangmiao, an assistant research fellow at the National Institute for South China Sea Studies, as saying China’s harvesting vegetables on the Paracel Islands "counters international theories, including those in a 2016 arbitration, that islands in the South China Sea could not support communities of their own."

In that 2016 ruling, judges of the Permanent Court of Arbitration (PCA) had rejected the infamous nine-dash line conjured up by Beijing to claim 90 percent of the East Sea, internationally known as the South China Sea. The ruling said that most geographical features in East Sea are not considered islands in accordance with the United Nations Convention on the Law of the Sea (UNCLOS).

The UNCLOS defines an island as a naturally formed area of land, surrounded by water, which is above water at high tide. It also states that rocks that cannot sustain human habitation or economic life of their own shall have no exclusive economic zone or continental shelf.

China seized the Paracel Islands from South Vietnam by force in 1974, and has been illegally occupying a number of reefs in the Spratly Islands since 1988.

Viet said: "We have on multiple occasions clearly stated that Vietnam has full historical evidence and legal basis to claim sovereignty over the Paracel and Spratly Islands in accordance with international law."