"All activities on the Paracel (Hoang Sa) and Spratly Islands without Vietnam’s permission are violations of Vietnam’s sovereignty, hold no value and are not beneficial to peace, security and stability in the East Sea. Vietnam resolutely opposes such activities," Foreign Ministry spokeswoman Le Thi Thu Hang said Thursday.

The East Sea is referred to internationally as the South China Sea.

Hang was responding to an inquiry regarding Vietnam’s reaction to China recently sending aircraft and warships to the Spratly Islands for a drill.

A video, posted August 4 on Haike News, a news app operated by the overseas edition of the People’s Daily, an official newspaper of the China’s Communist Party, said the Southern Theater Command had sent various aircraft to the Subi Reef for a drill that lasted over 10 hours. Exactly when the drill took place was not specified.

China had also sent a frigate and a corvette to the Mischief Reef on August 2, according to news site BenarNews.

"We once again affirm that the Paracel and Spratly islands are inseparable territories of Vietnam," Hang said.

Commenting on reports that China was building a surveillance network in the East Sea, Hang said the ministry would discuss the matter further with Vietnamese authorities.

On August 5, Forbes reported that China had been building a series of surveillance platforms spanning parts of the South China Sea. Research by the Asian Maritime Transparency Initiative said the surveillance platforms were part of what China calls the "Blue Ocean Information Network," the paper added.

Hang said: "Once again we stress that the maintenance of peace, stability and security in the East Sea is the interest and responsibility of all countries in the region as well as the international community. To achieve this goal, all countries should engage in activities with responsibility and goodwill."