In recent months, China has been celebrating the sixth anniversary of the formation of "Sansha City" with activities such as installing wave observation buoys around the Woody Island, organizing reality TV shows for children on the Paracels and carrying out scientific surveys on the islands.
Sansha was established on Woody (Phu Lam) Island in the Paracels in July 2012, administering several island groups including Vietnam's Paracel (Hoang Sa) and Spratly (Truong Sa) Islands.
Vietnam's Foreign Ministry spokesperson Le Thi Thu Hang said in a statement on Friday that the celebration activities seriously violated Vietnam's sovereignty over the Paracel and Spratly Islands, and went against the Vietnam-China Agreement on the Basic Principles Guiding the Resolution of Maritime Issues.
"Vietnam has full legal basis and historical evidence to assert its sovereignty over the Hoang Sa and Truong Sa Islands in accordance with international laws," Hang said.
She said that China's activities are not in line with the common perception reached by the two countries' leaders on the control of maritime disputes or the good development of bilateral relations.
These activities go against the spirit of the Declaration on the Conduct of Parties in the South China Sea and are not beneficial to the ASEAN-China negotiation of a Code of Conduct in the waters, as well as the maintenance of peace, stability, cooperation and development in the region, she said.
"Vietnam strongly opposes and demands that China immediately end these activities, and respect Vietnam's sovereignty over the Hoang Sa and Truong Sa Islands," Hang said.
Representatives of Vietnam's Foreign Ministry have reportedly met with representatives of the Chinese Embassy in Hanoi to discuss the issue.
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.