China is planning to institute an air defense identification zone (ADIZ) over the disputed South China Sea as the U.S. grows its military presence in the region and strengthens diplomatic relations with claimant countries, South China Morning Post (SCMP) reported Wednesday. China imposed similar zone in 2013 over eight uninhabited islands in the East China Sea, attracting criticism from Japan, South Korea and the U.S.

An air defense zone is a publicly defined area beyond national territory and gives the country authority to interrogate or intercept any unidentified aircraft before entering the country’s airspace. While ADIZs are not legally binding, commercial aircraft flying through the zone in the East China Sea are required to provide prior notice of their flight path.

“If the US military keeps making provocative moves to challenge China’s sovereignty in the region, it will give Beijing a good opportunity to declare an ADIZ in the South China Sea,” a source told SCMP.

The Chinese defense ministry told the newspaper that it was “the right of a sovereign state” to designate an ADIZ. “Regarding when to declare such a zone, it will depend on whether China is facing security threats from the air, and what the level of the air safety threat is,” the ministry told SCMP.

China has been building runways and ports on islands in the South China Sea to assert its claim over the region. The country is also planning to make islands in the Paracel archipelago a tourist hub, and it has already built sports facilities on its artificial islands in the contested area’s Spratly archipelago.

China has consistently defended its actions of growing military presence saying it does not have any intentions of starting a conflict and that its operations will add to the contested region's safety. The U.S. Navy has also been sending ships to the South China Sea under freedom of navigation patrols, angering Beijing. A top Marine Corps officer said earlier that the U.S. would continue its operations in the South China Sea and build trust with the countries in the Asia-Pacific region.

The South China Sea region has been long contested, with Beijing laying claims to most of it. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have conflicting claims to the waters, through which over $5 trillion of maritime trade passes annually. Beijing’s assertiveness in the disputed region has attracted criticism from several countries, including the U.S., which accuses China of militarizing the region.