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.

“In the event of war, any and all targets would probably be fair game for North Korea using any of its WMD tools,” Kim added.

While the size of the North’s stockpile is notoriously difficult to ascertain, the U.S.-based nonprofit Nuclear Threat Initiative, says the country is believed to be among the world’s largest possessors of chemical weapons. It estimates that the North ranks third — after the United States and Russia — with between 2,500 and 5,000 metric tons in its arsenal, the majority of which are nerve agents such as sarin and VX. At maximum capacity, the North is thought to be capable of producing up to 12,000 tons of the weapons.

But despite the massive amount, concerns over the North’s chemical threat have in recent years been largely drowned out by its growing nuclear weapons and missile capabilities.

Pyongyang conducted two nuclear tests last year and Kim Jong Un said in January that the country was in the final stages of preparations for an intercontinental ballistic missile test.

“The North’s chemical program has kind of fallen under the radar in most analysis about the threat perceptions emanating from the North, as most concerns — rightfully so — focus on the conventional programs and also the nuclear and missile efforts,” said J. Berkshire Miller, a Tokyo-based international affairs fellow at the Council on Foreign Relations.

“That said,” Miller added, “intelligence communities in the West and South Korea have warned for years about the dangers of the North’s chemical and biological weapons program and their potential use in asymmetric ways should the Kim regime feel threatened.”

While nuclear weapons are seen as a strategic deterrent meant to maintain the Kim dynasty’s grip on power, chemical arms would likely have an operational role in any wartime scenario, analysts say. Its rockets and missiles, including the intermediate-range Rodong with a range of 1,000-1,500 km, could be tipped with a chemical-laden warhead for strikes on much of Japan.

“It is possible that North Korea could target Japan with the missiles it has tested,” said Hamish de Bretton-Gordon, a former commander of the U.K.’s chemical and biological regiment who now works as a private consultant. “It is much easier to put VX in a warhead on a missile than to put a nuclear warhead on it. They could have a payload of up to 500 kg, which would be a considerable amount of VX and if fired at a city could create many casualties.”

In any war or looming conflict, U.S. bases in Japan would be tempting targets for chemical strikes as the North seeks to nullify America’s advantages in naval and air power.

But attacks on Japan and U.S. bases in the country, while possible, “would be out of desperation,” said Daniel Pinkston, a North Korea specialist at Troy University in Seoul, adding that inaccurate North Korean missiles would be unable to take out an airfield for long.

“It would degrade operations but they could decontaminate and resume operations,” Pinkston said.

Beyond the use of missiles, Pyongyang’s large number of special forces — skilled in infiltration techniques and likely trained in the use of chemical arms — would also be an option for delivering the weapons.

“I see the use in more of a terrorism lens for Japan — and there theoretically could be a worry about potential sleeper cells or illegitimate travelers trying to plan an attack during the Tokyo 2020 Olympics,” said the Council on Foreign Relations’ Miller.

Chemical terrorism has been a closely monitored concern for Japan since the Aum Shinrikyo cult’s sarin gas attack on the Tokyo subway system killed 12 and injured scores in 1995.

Experts, however, say even North Korea’s vaunted special forces would have a difficult time conducting such a strike.

“Those (kinds of attacks) are awfully hard to pull off with a mass effect, and Japan’s police agency is always watching for this sort of thing,” said James Schoff, an Asia expert at the Carnegie Endowment for International Peace.

The U.S. and Japan have also practiced their responses to a potential chemical attack by the North, but this training remains a small part of their overall joint exercises.

“This kind of preparation — and signaling this preparation — can be somewhat unsettling to the population but helps support deterrence,” said Schoff.

The existence of a North Korean chemical program has long stoked unease in Japan.

This was most recently highlighted in the wake of the Syrian regime’s August 2013 use of chemical arms in the country’s civil war, and U.S. President Barack Obama’s failure to enforce his “red line” warning to Damascus about using the weapons.

Just days after that attack, Chief Cabinet Secretary Yoshihide Suga stressed the significance of a united response, calling it “critically important” that the international community condemn the use of chemical weapons in Syria and that “in connection with countries such as North Korea, chemical weapons shall never ever be used again.”

The same week Suga made his remarks, then-U.S. Secretary of State John Kerry voiced similar concerns at a Senate hearing.

“North Korea is hoping that ambivalence carries the day,” Kerry said. “They are all listening for our silence.”

But despite Obama’s decision to ultimately back down from his threat, and the repercussions of that choice with its allies, the U.S. appears to have successfully negotiated those straits.

“I know that there was some discomfort in Tokyo about the Syria ‘red line’ failure, but it was not significant because most in power understood well that the U.S. would treat an attack on Japan … very differently from an attack on Syrians” said Carnegie’s Schoff. “I think that through our alliance conversations, the allies understand that part of the calculation is based on the extent of an attack.”

According to Schoff, an isolated chemical attack that leaves a few dozen people dead would certainly elicit a U.S. response, but perhaps not an immediate nuclear strike on North Korea. A large scale chemical weapon attack on city centers or U.S. bases in Japan, however, would trigger a much larger response that could be nuclear, if that was the only way to eliminate the North’s ability to launch follow-up strikes, he said.

Ultimately, though, if the use of VX by Pyongyang is confirmed, the assassination of Kim Jong Nam is likely to prove a “game-changer” in how the world deals with North Korea — and how it deals with the world.

“Pyongyang’s primary intention may have been to just get the job done, to eliminate Kim Jong Nam,” said Georgetown’s Kim. “But in doing so with a chemical weapon, the regime has shown the world it’s also capable of biochemical warfare, a tool that it can use as desired against any target.”

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