Chinese Foreign Ministry reiterated on Tuesday that Xisha and Nansha islands are within China's territory, saying Vietnam's claims are illegal and invalid. 

A diplomatic note sent by Vietnam's Permanent Mission to the UN on March 30 said Vietnam has "full legal basis and historical evidence to assert its sovereignty over the Spratly and Paracel Islands (Nansha and Xisha islands) in accordance with international law." 

Spokesperson Zhao Lijian said Vietnam's claims violate international laws including the Charter of the United Nations and the United Nations Convention on the Law of the Sea.