China firmly opposes any remarks and actions that violate its sovereignty over Xisha Islands and adjacent waters in the South China Sea, said Foreign Ministry spokeswoman Jiang Yu on Friday.

Jiang made the comment after Vietnamese foreign ministry spokeswoman Nguyen Phuong Nga said Thursday, according to media reports, that Chinese vessels' seismic exploration activities near Xisha Islands had violated Vietnam's sovereignty.

"China has indisputable sovereignty over Xisha Islands and adjacent waters," Jiang reiterated in a news release.