U.S. guided-missile destroyer USS Lassen sailed within 12 nautical miles of at least one of the artificial islands in the South China Sea claimed by China on Tuesday, bringing to stark reality the growing tensions between the U.S. and China.

For some two hours, the USS Lassen sailed close to the 12 nautical-mile area claimed by China as its territory, at one point sailing within the 12 nautical miles of Subi Reefs, while two Chinese vessels shadowed the guided-missile destroyer. The episode went without a military clash, but U.S. said that it would repeat such sail-bys, and Beijing, next time, might do more than call in the U.S. ambassador.

The U.S. argues that such sail-pasts are necessary to demonstrate the U.S. commitment to keeping the international waters free. In a move to bolster its territorial claims in the South China Sea, China has been reclaiming reefs and tiny islands into artificial islands. However, international laws do not recognize territorial sea claims emanating from man-made islands built on previously submerged reefs.

Tuesday’s incident was a foreseeable one: The U.S. rebalance in East Asia and the growing maritime power of China were bound to become a point of conflict at some point. In fact, Washington is reported to have deliberated for several months such “freedom of navigation” patrols in the area, through which one-third of global trade passes.

Seoul should have been aware of an impending incident in the South China Sea. Despite Foreign Minister Yun Byung-se’s denial that the South China Sea situation was ever discussed during the summit meeting between President Park Geun-hye and U.S. President Barack Obama, Obama’s remarks at the Oct. 16 joint press conference indicate that the two leaders did talk about the issue. In hindsight, Obama appears to have been alluding to the possibility of U.S. action, urging Korea to take a stand with the U.S. when he said, “Where China fails to abide by international norms and rules, we expect the Republic of Korea to speak out on that, just as we do.” 

In fact, Obama pointed out that it would be in the interests of Korea to speak out:  “(G)iven the size of China right there on your doorstep, if they’re able to act with impunity and ignore rules whenever they please, that’s not going to be good for you — whether that’s on economic issues or security issues.”

Such clear and strongly worded remarks from Obama should have alerted the Park administration to the likelihood of impending U.S. action against China and diplomatic and security officials should have scurried to formulate a contingency plan. Instead, in an answer to a National Assembly lawmaker, Yoon said that the South China Sea issue never came up during the summit.

The government’s response to Tuesday’s incident in the South China Sea was rather pedestrian and ambiguous. Without issuing a formal statement, a senior Blue House official, asked to comment by reporters said, “South Korea has been strongly calling for restraint of any action that affects peace and stability in the region,” adding that disputes should be resolved according to international norms. When the next incident erupts, Seoul ought to have a clearer response ready.

The government is in a great quandary as its ally, the U.S., and its biggest trading partner, China, are increasingly at odds. However, the answer is not all that difficult to arrive at if the administration stays focused on the pursuit of what is in the best interests of the country. As a country which relies on the South China Sea shipping route for 30 percent of its exports and 90 percent of energy shipments, it is of vital interest to Korea that the shipping lanes remain free. Efforts to restrict freedom of navigation should be strongly protested.