US Secretary of Defense Ashton Carter landed aboard US aircraft carrier  USS John C Stennis in the contested waters of the South China Sea on Friday, an apparent move to flex the country's military muscles.

To reinforce Washington's rebalance to Asia strategy, under the guise of maintaining the freedom of navigation, the US has constantly sent warships and bombers to the waters surrounding the islands claimed by China.

In a recent op-ed in the Financial Times, John McCain, a US senator and chairman of the Senate Committee on Armed Services, urged Washington to consider fresh policy options such as enhancing military postures across the Asia-Pacific region.

In face of the ever upgrading of military provocation from the US, China should show its explicit stance. China can set a red line for the US and make clear to Washington that if it continues to infringe China's core interests by challenging China's territorial claims and not respecting its sovereign rights, it should be aware of a dangerous showdown with China.

In case of the US' expanding patrols and surveillance, China can adopt more active measures to dispel them.

If the US acts on its will to actually go to war with China, the Chinese military will not hesitate to take countermeasures.

It is abnormal that the US military shows up in the waters so frequently. As an external power far distant from the South China Sea, it is behaving in a much more high-profile manner than the regional stakeholders.

It is also instigating regional countries and outside forces to raise tensions. Washington has become the decisive factor for the heightened tensions in the South China Sea.

China is exercising its sovereignty while the US is grappling for a sphere of influence in the region.

Even when there are sovereignty disputes over the islands, claimant countries do not wish to see the tensions intensify.

The US has strategic motives behind its provocative actions in the South China Sea.

To what extent the uncertainties in the South China Sea will evolve is determined by how high a wave the US will create.

Though China is reluctant to see it, a military clash could be dangerously triggered by accident given the Pentagon's frequent and escalating military provocation. But it will not happen unless the US crosses the red line.