It its latest attempt at sabre-rattling, North Korea has threatened to shoot down a South Korean airliner during next week’s exercises between ROK military forces and their American counterparts.

Reuters has the warning, issued by the official Korean Central News Agency:

“Security cannot be guaranteed for South Korean civil airplanes flying through the territorial air of our side and its vicinity … above the East Sea of Korea (Sea of Japan) in particular, while the military exercises are under way,” the North’s KCNA news agency quoted a statement from a government official as saying.

In response, South Korean airlines have announced plans to re-route flights approaching Seoul from the east, placing them farther away from North Korean territory. Singapore Airlines, which also operates a number of flights into and out of Seoul, has adopted a similar policy. Other carriers, including Japan Airlines, All Nippon Airways and Air China, said they have no plans to alter their flight routes.

There was no word from U.S. carriers that service South Korean destinations, including Northwest Airlines and United.

Pyongyang’s warning is almost certainly a prelude to the expected launch of a Tapeodong-2 long-range missile, now being prepared at a test site on North Korea’s east coast. DPRK officials claim the rocket will be used to put a satellite into orbit, but western analysts dispute that statement. There were no signs of a satellite deployment during previous TD-2 launches in 1998 and 2006. Intelligence officials in the U.S., Japan and South Korea believe the launch is nothing more than a test of the extended-range missile, capable of hitting U.S. territory throughout the Pacific.

North Korea is expected to announce a “closure area” for air and naval traffic in preparation for the test. The restricted area may extended into commercial air corridors over the Sea of Japan –the same routes used by airliners flying into Seoul from the east. However, the launch of a single missile, from a location on the North Korean coast, would pose a minimal threat to commercial air traffic.

But the warning statement–and anticipated closure area–will achieve an important goal: minimizing air traffic over the Sea of Japan during the upcoming missile test. That will make it for North Korean air defenses to keep tabs on U.S. platforms expected to monitor the launch, namely the RC-135S “Cobra Ball,” and the RC-135V/W “Rivet Joint.”

Cobra Ball is a dedicated Measures and Signatures Intelligence (MASINT) aircraft, configured to track ballistic missile flights at long range. Normally based at Offut AFB, Nebraska, at least one RC-135S will be deployed to Kadena AB, Japan in preparation for the North Korean test. Rivet Joint is a dedicated SIGINT platform, used to monitor enemy communications and threat emitters, providing additional threat warning to Cobra Ball and other allied assets.

Indeed, the greatest risk to our reconnaissance platforms–and commercial airliners–comes from North Korean fighters and long-range surface-to-air missiles (SAMs), not the TD-2. The DPRK maintains a number of older fighters, mostly MiG-21s and MiG-19s, on alert at bases on it eastern coast. While both have limited ranges, they could (potentially) intercept an RC-135 operating within 150 NM of the DPRK coastline, or a commercial jet approaching ROK airspace.

A second threat comes from the aging SA-5 “Gammon” SAM system, purchased from Russia more than 20 years ago. North Korea has two SA-5 complexes, located an Ongo-dak and Tokchae-san. Together, they provide overlapping coverage of the eastern coast, and airspace south of the DMZ. With a range of at least 150 NM, the SA-5 is optimized for engagements against large, non-maneuvering targets like reconnaissance aircraft and commercial airliners.

In response, Washington and Seoul should make it very clear that any provocative move by Pyongyang will result in a strong military response. The U.S. and South Korea have a variety of assets that could target the SA-5 sites and airfields housing MiG-21s and MiG-19s. If North Korea sends its fighters on an intercept mission, they should be shot down. If one of the SA-5 complexes “paints” a recce flight or an airliner, the site will be hit with an ATACMS, anti-radiation missiles, cruise missiles or a combination of those weapons.

It’s no accident that North Korea has grown increasingly bold in its provocations toward the U.S. and our allies in the Far East. Sensing weakness and indecision in the Obama Administration, Kim Jong-il is quite willing to test the limits of our patience–and response options.

Less than two months into Mr. Obama’s term, Pyongyang has announced plans to launch another TD-2 (on a flight path that may carry it over Japan); vowed military against South Korea, and threatened to disrupt commercial air service along busy east Asia corridors.

The U.S. response? Nothing more than mild diplomatic warnings. No wonder Mr. Kim is feeling his oats.