The US has spent at least $40 billion on a missile defense system intended to knock down or deter incoming North Korean intercontinental ballistic missiles, but actually using the system could lead to an accidental nuclear war with Russia, according to an expert.

Jeffrey Lewis, the founding publisher of Arms Control Wonk, took to Twitter to detail how the US could find itself exchanging nuclear salvos with Russia if it ever tried to shoot down an incoming North Korean ballistic missile.

The US’s Missile Defense Agency, which operates the Ground-based Midcourse Defense (GMD) missile shield, told Business Insider in May that in the event of a real incoming threat, they would launch several interceptors to increase the chances of knocking out the missile.

Lewis pegs this figure at about four or five interceptors.

But only one interceptor missile could hit the threat. The others would continue streaking through the high atmosphere towards Russia and China.

Read the whole story from Business Insider.

Featured image courtesy of Russian Presidential Press Service