Last week's stunning revelation that the deadly VX nerve agent was used to kill the estranged half brother of North Korea's leader at a crowded air terminal in Malaysia has thrown a spotlight on Pyongyang's chemical weapons arsenal — and raised questions of whether the operation was a purposeful but deniable signal to its enemies, including Japan.

The claim that VX, deadly even in minuscule amounts, was employed in the Feb. 13 attack has contributed to the widespread belief that Pyongyang had sent a hit team to assassinate Kim Jong Nam, the older sibling of leader Kim Jong Un. The North, which is not party to a global chemical weapons convention that prohibits their production, stockpiling and use, has denied that it possesses such an arsenal. But experts say the VX was almost certainly manufactured in an advanced state-run weapons lab.

"If North Korea was behind the assassination, it has just unveiled a glimpse of its chemical warfare capability to the world," said Duyeon Kim, a Seoul-based researcher at Georgetown University's Institute for the Study of Diplomacy.