South Korea is increasingly concerned that North Korea's latest threats about processing plutonium to expand its nuclear weapons arsenal is no longer a negotiating ploy to gain leverage with the US.

Policymakers in Seoul believe Pyongyang may have decided to pursue a non- negotiable strategy of trying to develop nuclear-tipped ballistic missiles by 2012, in an attempt to bolster the ailing regime with a fully fledged nuclear deterrent and secure a domestic propaganda coup.

Washington and Seoul have usually interpreted bouts of belligerence from the communist dictatorship over recent years as attempts to bargain for food aid, fuel oil and security guarantees, particularly in the context of the stalled six-party talks aimed at denuclearising the Korean peninsula.