The United States on Friday announced it will expand its missile defense system in response to what it called “faster-than-anticipated” North Korean nuclear weapon development.

The Pentagon said it would spend $1 billion to double the number of ground-based missile interceptors to be deployed on the US West Coast to 14.

There are currently 26 long-range missile interceptors based at Fort Greeley in Alaska and four at Vanderberg Air Force Base in California but the latest announcement means that there will be a total of 44 by 2017.

US Defense Secretary Chuck Hagel said Washington wants to “stay ahead” of recent threats of a nuclear strike from North Korea

Hagel also said Friday that US missile defense systems in place provide protection from “limited intercontinental ballistic missile (ICBM) attacks,” but added, “North Korea, in particular, has recently made advances in its capabilities and has engaged in a series of irresponsible and reckless provocations.”

US Secretary of State John Kerry conveyed the Pentagon’s intentions to his South Korean counterpart, Foreign Minister Yun Byung-se, and reiterated the importance of the US-Korea alliance during a telephone call on Saturday.