The U.S. Secretary of Defense has ordered the U.S. military to develop options for more assertive freedom of navigation (FON) operations around China's man-made islands in the South China Sea. There are significant legal, operational and political risks involved with these operations.

The legal situation regarding China's claimed features in the South China Sea is messy. The claims overlap with other countries that have also undertaken extensive reclamation works on their occupied features, including building airstrips and adding military fortifications. But the U.S. only appears concerned with what China has done. The U.S. thus risks giving the impression that it has moved away from a position of neutrality in the sovereignty disputes.

Then there are issues associated with the status of the features before reclamation works were undertaken. Some were previously submerged at high tide, in which case — under international law — they are only entitled to a 500-metre safety zone around them. Others may have had a few rocks or sandbanks above water at high tide, which means they are entitled to a 12-nautical-mile territorial sea with no right of overflight above them. Some land features could even be large enough to justify wider claims to maritime zones. The situation is further complicated by the fact that some of China's occupied features are in close proximity to features occupied by other countries.

The status of particular features in the South China Sea has long been a vexed issue for geographers. In undertaking FON operations, the U.S. is going to have make decisions on a case-by-case basis about what type of challenge is being made around each feature. Is it exercising a right of innocent passage through a possible territorial sea, or is it flying or sailing close by a feature that is only entitled to a 500-metre safety zone? A clear judgment is possible with some features but uncertainty surrounds others.

Further problems arise if the U.S. decides to exercise innocent passage around features that may have a legitimate territorial sea. Patrolling into another country's territorial sea, loitering in the territorial sea, or diverting from the normal passage route between points A and B just to demonstrate a right of passage, do not constitute innocent passage. The UN Convention on the Law of the Sea (UNCLOS) makes clear that innocent passage should be 'continuous and expeditious', and should not involve 'any threat or use of force against the sovereignty, territorial integrity or political independence of the coastal State'.

FON operations are inherently dangerous. They may lead to close encounters both between warships and between aircraft. Before embarking on more assertive activities, the U.S. must be confident that its ship and aircraft captains are capable of exercising the high standards of seamanship and airmanship required. But this may not be the case. Even in the best run organisations, adrenalin can start flowing with a close encounter and misjudgements occur without top-level skills and experience. Manoeuvring a warship safely near to other vessels requires different skills to those needed for operating its weapons and systems.

Then there's the issue that just like on the road, a good driver can still be involved in an accident caused by a bad driver. The U.S. has often criticised Chinese vessels for lacking professionalism and failing to follow the international rules for preventing collisions. But the U.S. Navy has experienced several accidents in recent years as a consequence of its own navigational errors and poor seamanship.

In the air, an error of judgment by one pilot can lead to a collision and both aircraft crashing. But while the U.S. and China have agreed to a supplementary agreement relating to rules of behaviour for managing encounters between surface ships, they have not yet come to a similar agreement for air encounters. This is unfortunate as air encounters carry the highest operational risks.

Politically, while more aggressive U.S. actions might play to the American domestic audience, there is no certainty that regional audiences will be as supportive. After initial reports of more assertive FON operations by the U.S., a spokesman for the Vietnamese foreign ministry urged all parties concerned to respect the sovereignty and jurisdiction of coastal states in accordance with international law and not to further complicate the status quo. Both the U.S. and China may have been his target. With its own excessive claims to maritime jurisdiction under international law, Vietnam is often also the target of American FON operations.

As we have seen in the past with the littoral countries' reaction to the Regional Maritime Security Initiative in the Malacca Strait, and regional implementation of the Proliferation Security Initiative, the U.S. can fail to appreciate regional sensitivities to maritime sovereignty and law of the sea issues. More assertive FON operations could similarly be regarded as an overbearing unilateral assertion of rights by Washington. The U.S. is particularly vulnerable to these criticisms because it is not a party to UNCLOS.

The U.S. may be giving insufficient consideration to the impact of more assertive FON operations in the South China Sea on regional stability. By provoking China in such an aggressive and unnecessary manner, it can only make the current situation worse. For all these reasons, I hope that Washington will tread carefully on the issue of implementing a more aggressive FON program in the South China Sea. It was encouraging in this regard that U.S. Secretary of Defense Ash Carter took a less confrontational tone in his address to the recently concluded Shangri-la Dialogue in Singapore.

The author is an adviser to the Maritime Security Programme at the S. Rajaratnam School of International Studies (RSIS), Nanyang Technological University