China on Tuesday condemned the recent actions taken by Vietnam on the Nansha Islands, saying they constituted an encroachment upon China's territorial sovereignty.

"China has indisputable sovereignty over the Nansha Islands and their adjacent waters," said Foreign Ministry spokesperson Jiang Yu during a regular press briefing.

Her comments came in response to a question concerning Vietnam's recent holding of elections for so-called "National Assembly deputies" and "People's Council representatives" on the Nansha Islands.

"Any one-sided action taken by any country on the Nansha Islands is illegal and invalid," said Jiang, adding that the elections infringe on China's territorial sovereignty and sovereign rights and are not in line with the spirit of the Declaration of Conduct of Parties in the South China Sea (DOC).

The DOC was signed in 2002 as a code of conduct for all parties involved in diplomatic issues in the South China Sea.

Signatories to the DOC agreed to settle disputes over territory in the South China Sea through friendly coordination and negotiation, and to exercise self-restraint in the conduct of activities that would complicate or escalate disputes and affect peace and stability in the region.