A United States defence official told CNN television network that the destroyer USS Lassen "conducted a transit" within 12 nautical miles (nm) of Subi Reef in the Spratly Islands on Tuesday morning local time.
The US claims that its action is justified as exercising freedom of navigation in waters which it does not deem as China's territorial sea, as Subi Reef is regarded by the US as a low-tide elevation, and hence not entitled to its own territorial waters. The decision to sail the USS Lassen close to the disputed isle is no doubt due to the domestic pressures the US faced, after China started to reclaim land in the features under its control in the Spratlys.
Through the "Lassen" transit, the US intends to send a message to its allies in South-east Asia, especially the Philippines, that it is prepared to engage in a show of military force towards China. This move no doubt will encounter China's protest, while the reaction from South-east Asia and other parts of the world will be mixed.
There are some key differences in viewpoints that lead to China and the US viewing the disputes in the South China Sea differently.
While both China and the US claim that freedom of navigation in the South China Sea is significant, and both sides endeavour to secure such freedom, the two countries obviously have a different interpretation of the scope of freedom of navigation under the 1982 United Nations Convention on the Law of the Sea (Unclos).
China in fact has never signalled that it intends to obstruct commercial shipping or flights across the South China Sea.
The US view is that freedom of navigation goes beyond merely commercial shipping. China holds that types of military activities in foreign countries' Exclusive Economic Zone (EEZ) - such as those that might have an impact on marine environment, or share a similar nature as marine scientific research - should not be viewed as freedom of navigation. China is not the only country in the South China Sea that is sceptical about military activities in its EEZ. Malaysia also objects to military exercises in its EEZ.
The legal status of Subi Reef is also not determined. It's too early to jump to the conclusion that it does not enjoy 12 nm of territorial sea.
Then there is the question of "innocent passage". If the US were to send more military vessels to patrol or transit through other features in the Spratlys deemed a rock - and hence entitled to claim 12 nm of territorial sea - the principle of innocent passage should be strictly respected.
But China may want the US to read between the lines of Article 19 of Unclos: "Passage is innocent so long as it is not prejudicial to the peace, good order or security of the coastal State. " One may consider the Lassen's passage as the equivalent of the US flexing its muscle at a clear target, China, and consider it prejudicial to China's peace.
As for land reclamation, China has made several official statements that its land reclamation will be used for civilian purposes, providing international public goods for search and rescue and so on. The military function will be activated only when it feels it is being threatened and will be used for defensive purpose only.
To what extent subsequent patrols or transits by US ships will be read as threatening China's national security is a question for both countries to consider.
Beyond the US and China, it is the South-east Asian region that has to deal with the new situation.
Asean is working with China on negotiations to draft a Code of Conduct. Asean is hoping to solve the problems in the South China Sea within the Asean framework. Many of its member states which are not a party to the dispute always wish to keep a balance between the US and China.
The Philippines, which also claims Subi Reef, might feel relieved at the US challenge to China's maritime claims. The reaction from other claimant states, Vietnam, Malaysia and Brunei remains unclear.
As announced, the US is also likely to sail ships close to features occupied by Vietnam and the Philippines. In doing so, it wishes to dispel China's sceptical view that is picking on China as the only target. America does not want to be interpreted as taking sides in the South China Sea dispute. The Chinese government, academics and netizens have often pointed to the fact that China was not the first or only country to build on or reclaim land in disputed territories, and argued that other claimants moved much further than China to consolidate their claims through many approaches.
The Lassen move is certainly a major move from the US. But it should come as no surprise to China, given the domestic pressures within the US calling for such freedom of navigation exercises to sail within 12 nm of features that China claims.
China's protest over the American action was also predictable. The two countries - one a major claimant state and the other a major user state and stakeholder - have to respect each other's interests and understand each other's concern.
What is absolutely undesirable to both countries is any further provocation that may lead to escalation of tension. While it may be legally justified, China has to consider the political implications arising from its land reclamation activities on disputed territories. It has to stick to its principle of using its facilities for civilian purposes and sharing the environmental impact assessments on the land reclamation activities.
The US has to understand that China's concern over its new move is not about the interpretation of the scope of freedom of navigation. Instead, its concern rests on the question of US neutrality on the dispute settlement, and the risks of militarising the South China Sea.
Convergence of interests for China, for the US, and for the South-east Asian region is the way forward, so the parties can figure out ways to enhance maritime cooperation and reduce the risks of further tension. One urgent need now is working on how to avoid accidents at sea, given the likely increase of US patrolling activities in the vicinity of the Spratlys areas, and the likelihood of China's vessels following and monitoring such patrolling and transiting.
- The writer heads the Institute for China-America Studies, an independent, non-profit academic institution launched by the Hainan Nanhai Research Foundation. She is also a research fellow with National Institute for South China Sea Studies and China Institute, University of Alberta.