South Korea and the United States are reportedly close to a missile deal that would allow Seoul to extend its ballistic missile range from the current 300 km to 800 km, while leaving its payload limit intact at the current 500 kg.

If the missile range is lengthened as reported, South Korea would be able to hit any position in North Korea from bases located north of Daejeon, a city at the center of the nation.

This would be a big enhancement in Seoul’s striking capability. Yet it still falls short of meeting Seoul’s demand. It wants a minimum range of 1,000 km to be able to cover any place in the North from its southernmost territory.

Washington has sought to set the range at 550 km to 600 km, saying it would be enough for the South as the North’s ground forces are concentrated below the line linking Pyongyang and Wonsan.

Regarding the missile payload, Seoul has demanded that the maximum weight be raised to at least 1,000 kg. This is necessary as a missile’s accuracy falls when its range is lengthened. To offset the drop in accuracy, the destructive power of the missile needs to be enhanced, which can be achieved by making the warhead bigger.

Washington is against anything more than 500 kg on the grounds that a missile above that ceiling can carry a nuclear warhead. For this reason, it notes, the Missile Technology Control Regime limits missile exports and technology transfers to those with a payload weighing less than 500 kg.

Yet Washington’s stance is hard to accept. In the first place, there is little or no possibility of South Korea developing a nuclear warhead. And Seoul is not a signatory of the MCTR. Furthermore, a payload of 500 kg cannot knock out major military facilities of the North, which are mostly built deep under the ground.

And the North has been escalating its missile threat. Its Rodong missiles, which have a range of 1,300 km, have the whole of South Korea within reach. It has also deployed 3,000-km medium range missiles and is testing intercontinental ballistic missiles.

All this justifies a significant increase in the payload cap, which was set at 500 kg in 1979 when North Korea had no nuclear capabilities. It remained unchanged when the two sides rewrote the missile guidelines in 2001.

According to reports, Washington has allowed Seoul to more than double the payload of unmanned aerial vehicles, which is also set at 500 kg, in return for freezing that of missiles. Yet UAVs and missiles are totally different weapons systems.

For South Korea, while it is important to extend the missile range and increase the payload weight, a more urgent task is to have a missile defense system in place. The urgency is all the greater given North Korea’s persistent efforts to miniaturize its nuclear warheads to mount them onto its missiles.

Yet the South remains highly vulnerable to the North’s missile threats. Currently, the only missile interceptors deployed in the South are the 48 secondhand Patriot PAC-2 systems Seoul purchased from Germany in 2007. But the ability of these old weapons to intercept incoming missiles is limited.

Against this backdrop, Washington has been urging Seoul to participate in its global missile defense system. Last week, it agreed with Tokyo to place a new missile defense radar system on Japanese territory to defend against a ballistic missile threat from North Korea.

But Seoul has opted to stay out of the U.S.-led missile defense system for strategic reasons and is seeking to build its own system that is focused on the Korean Peninsula. This is a worthy goal but not easy to achieve.

Last year, Seoul developed a medium-range surface-to-air missile aimed at intercepting aircraft flying at an altitude between 10 km and 15 km. Defense officials said they would upgrade the missile, dubbed the Cheongung, into a missile interceptor similar to the Patriot PAC-3.

The project is highly likely to be fraught with technical difficulties and therefore will take time to finish. This means the military will have to find other ways to enhance its missile defense capabilities.