WASHINGTON—The Pentagon will spend $1 billion to expand the West Coast-based missile-defense system in a direct response to provocations by North Korea and rising tensions on the Korean peninsula, officials said Friday.

By 2017, Defense Secretary Chuck Hagel said the U.S. would install 14 additional ground-based missile interceptors at Fort Greely, Alaska, representing an increase of nearly 50% over the 30 interceptors now located both there and in California.

The move accentuates new worries that North Korea has accelerated progress in its intercontinental ballistic missile program.

The precise ranges of North Korea's missiles are uncertain. Defense officials currently believe that North Korean missiles can reach Hawaii as well as Alaska, but not the continental U.S. At the same time, U.S. officials don't believe North Korea has developed a miniaturized nuclear warhead that could be mounted on any missile.

Mr. Hagel didn't specify when U.S. military and intelligence analysts believe Pyongyang will have an ICBM capable of carrying a nuclear warhead. The purpose of Friday's announcement was to keep ahead of Pyongyang's military developments, Mr. Hagel said.