Vietnam has called on the international aviation community to condemn China’s act of sending planes unannounced to a disputed reef in the South China Sea, Tuoi Tre News, a Vietnamese news agency reported Sunday.

Vietnam reportedly logged 46 such incidents — which the country says endangers air safety and violates its sovereignty — in the first week of January, and has also sent letters of protest to China and the International Civil Aviation Organization (ICAO) over the issue.

The Civil Aviation Authority of Vietnam (CAAV) sent letters to the ICAO Wednesday and Friday, asking the organization to devise measures to prevent similar moves by China, Tuoi Tre News reported. CAAV also reportedly issued notices to several other aviation bodies and over 100 international carriers, urging them to protest China’s actions.

“We are working hard to closely monitor flight activities and ensure air safety in the airspace managed by Vietnam,” CAAV said, according to Tuoi Tre News.

A report by BBC said that China has been conducting test flights to the Spratly Islands, where Beijing has been building an artificial island to accommodate a runway, among other things.

The Spratly Islands are located in a section of the South China Sea that's been a matter of contention between China, Taiwan, Vietnam, Philippines, Brunei and Malaysia, all of whom lay claim to parts of the region and have ongoing disputes with China, which has grown increasingly aggressive in recent months in asserting its claim to the region.

“ICAO is responsible for supervising all civil aviation activities in the world, and we expect that it will issue warnings to China after it finds out about its violations,” Lai Xuan Thanh, the director of CAAV, said in an interview to the Wall Street Journal Friday. Lai also said that China’s planes had taken the route used by several international flights though none of them changed their flight paths over the incident.

Last Sunday, China rejected Vietnam's claims that it had violated the latter's airspace and said that China “has indisputable sovereignty over the Nansha Islands and their adjacent waters.” Hua Chunying, China’s foreign ministry spokeswoman, reportedly said that it will not accept Vietnam’s claims, calling them “unfounded accusations.” A spokeswoman for the U.S. Department of Defense condemned China’s flights and said, according to the Journal, that the flights “are inconsistent with the region’s commitments to exercise restraint from actions that could complicate or escalate disputes.”