China on Monday rejected a complaint from Vietnam that China had failed to notify it about flights to an island it has built in disputed waters in the South China Sea, saying it was Chinese territory and it did not need to notify anyone.
Chinese civilian aircraft have conducted several test landings on Fiery Cross Reef, one of three runways China has been building for more than a year by dredging sand up onto reefs and atolls in the Spratly Islands.
Vietnam and the Philippines have both objected to the flights and the United States, which has criticised China's construction of islands in the South China Sea, has expressed concern about an increase in tension in the region.
Vietnam says China's landings were on what it calls an "illegally" built reef, and has vowed to defend its sovereignty through peaceful measures.
Vietnam's civil aviation authorities also said China's aircraft flew into its "flight information region" without prior notification and "flight operations of Chinese aircraft have threatened safe exploitation of international air routes."
China's Foreign Ministry spokesman Hong Lei said that complaint was "groundless" and reiterated that China had sovereignty over the area.
"According to international law, national aviation activities are not subject to relevant restrictions from international civil aviation conventions and the International Civil Aviation Organization," Hong told a regular briefing.
China had notified Vietnam about the flights in any case, he said.
China's Xinhua news agency last Wednesday announced two test flights to the island, four days after it angered Vietnam with its first landing on the runway.
China claims virtually the whole of the South China Sea.
Each year more than $5 trillion of world trade is shipped through the South China Sea, where Brunei, Malaysia, the Philippines, Vietnam and Taiwan have rival territorial claims.