As I suspected, the South Korean government’s statement that it would join the Proliferation Security Initiative may be an empty threat:

South Korea on Sunday failed to make good a threat to join a U.S.-led initiative aimed at preventing the spread of weapons of mass destruction the moment North Korea goes ahead with its rocket launch.

An official statement on Sunday’s launch by Foreign Minister Yu Myung-hwan made no mention of the Proliferation Security Initiative, a grouping of countries who agree to intercept ships suspected of carrying WMD or related materials.

A government official said the statement did not mention the PSI, because Seoul was worried about “unnecessarily heightening tensions” given that North Korea “is extremely sensitive about the PSI.”  [Chosun Ilbo]

Seoul is giving themselves some wiggle room though to possibly join the PSI in the future:

Some officials had apparently argued against mentioning the PSI, saying the step should not be presented as a punitive action against North Korea, which could only reinforce Pyongyang’s notion that it is the sole target of the initiative. Instead, Seoul should present PSI membership as a move to join international efforts against proliferation.

Another government official said Seoul has already decided to join, but when to join is “a matter of flexibility.” A senior Cheong Wa Dae official said, “The government has already made clear that the policy is to join the PSI. The process is underway and we’re moving in that direction. What matters now is when to join. We’re going to join the PSI not because North Korea has launched a rocket but based on our own schedule, though the plan is already sitting on the conveyor belt.”

Now ask yourself, even if South Korea joins the PSI does anyone really think they will begin inspecting North Korean ships for WMD materials?