The British government has directly accused Russia of using a very sophisticated chemical weapon — a “poison gas” in common idiom — in a failed attempt to murder a former Russian defector and his daughter.

A vengeful Kremlin assassination team prowling Britain sounds like a scene in a Cold War spy novel and the botched March 4 homicide has Cold War echoes. The targets, former Russian spy Sergei Skripal and his daughter, Yulia, were sitting on a park bench in Salisbury, England.

However, immediate 21st century contexts matter. Vladimir Putin’s Russia is an especially relevant context. Putin’s Kremlin is currently engaged in global political and cyber agitation while waging so-called “hybrid war” in Ukraine and Syria.

Putin’s Kremlin practices what some analysts call “gray zone warfare.”

Waging a gray zone campaign requires maintaining “plausible deniability” — in order to escape retribution, be able to deny responsibility for the dirty and destructive operations.

Propaganda, crime, covert influence operations, cyber intrusions and old-fashioned bribery are gray zone weapons.

The Putin-led Kremlin employs all of them and more. The April-May 2007 Russian sustained cyber assault on Estonia illustrates plausible deniability. Estonia traced the economy-crippling attacks to “state agencies in Russia.” Russia denied the charge, attributing the attacks to criminals and vandals.

Violence is an integral gray zone tool. In Ukraine, Russia has used agitators, mercenaries, assassins, special operations soldiers and occasionally Russian conventional forces. But violence is risky. In order to avoid international reprisals that seriously damage Russian interests, gray zone violence must be constrained. The bloodshed must be kept below that hazy threshold where an adversary suddenly retaliates with damaging consequences.

More or less, Russia has managed to do that in Ukraine. Russia’s invasion of Georgia in 2008 stayed below the threshold. That invasion mimicked the “creeping war of aggression” Serbian dictator Slobodan Milosevic launched in 1991 when Serbia attacked Croatia. Serbia would launch an attack, take a small piece of territory, and then hunker down to absorb the political blowback from the UN and Western Europe.

Putin’s Kremlin has employed assassins in Western Europe. Since 2003, 14 people in Britain with Russian connections have died under mysterious circumstances. They were either Russian expatriates (several were former intelligence agents) or individuals with connections to Russian businesses or opposition political figures. Putin critic Alexander Litvinenko is perhaps the most famous. In 2006 the former security officer drank tea poisoned with polonium-210 and died in agony. In 2016, British investigators concluded that it was “highly probable” he was assassinated by the FSB — Russian domestic security service.

But the use of an illegal chemical weapon that could be employed on a battlefield makes the March 4 crime qualitatively different. The assassins used Novichok-A-230, an “enhanced” nerve agent dispersible as a liquid or powder. Reports claim it is eight times more toxic than VX liquid nerve agent. In February 2017 North Korean assassins used VX to murder Kim Jong Nam, dictator Kim Jong Un’s half-brother.

I think this is one reason British Prime Minister Theresa May has framed the March 4 incident as no ordinary assassination. May argued that the incident can be characterized as a state-directed chemical weapon attack that occurred on British territory — in other words, an act of war. She mentioned invoking NATO Article 5 as a response to incident.

NATO Article 5 — also called The Three Musketeers Clause — commits the alliance to defend an ally when its territory is attacked. The daring French musketeers promised one for all and all for one. Article 5 makes a similar serious commitment. It has only been invoked once: after al-Qaida’s attack on the U.S.

I doubt that Britain will invoke it. However, Britain is telling Putin’s Kremlin “gray zone war” is still war. And the March 4 incident is a very pale white shade of gray.

Austin Bay is a syndicated columnist and author.

Austin Bay