In Defense Secretary Chuck Hagel's announcement Friday, he said he's determined to ensure protection of the U.S. homeland and stay ahead of the North Korean missile threat.
The plans to boost defense include spending $1 billion to add 14 interceptors to a West Coast-based missile defense system. Hagel acknowledged that the interceptors already in place to defend against potential North Korean missile launches have had poor test performances.
The Pentagon plans to add the new interceptors to 26 already in place at Fort Greely, Alaska, which will expand the system's ability to shoot down long-range missiles in flight before they could reach U.S. territory. In addition, the U.S. also has four missile interceptors at Vandenberg Air Force Base, Calif.
Hagel said the new additions will be in place by September 2017, but they will not be deployed until they have been thoroughly tested.
James Miller, the undersecretary of defense for policy, and Hagel said the U.S. will conduct environmental studies on three potential locations for interceptors in the United States, including on the East Coast.
Miller said the studies would provide options for building an interceptor base on the East Coast or adding more interceptors in Alaska, should either approach become necessary due to further future increases in the threat from Iran and North Korea.
The missile defense sites in Alaska and California were built during the administration of President George W. Bush as a reaction to the threat of a missile strike from North Korea.
In a speech Tuesday at the Atlantic Council, Miller said North Korea launched a satellite into space last December, demonstrating its mastery of some of the same technologies required for development of an intercontinental ballistic missile.
"Our concern about Pyongyang's potential ICBM capability is compounded by the regime's focus on developing nuclear weapons," he said. "North Korea's third nuclear test last month is obviously a serious concern for all nations."
North Korea recently threatened to reduce Seoul to a "sea of fire" and stage pre-emptive nuclear attacks on Washington.
"North Korea's shrill public pronouncements underscore the need for the U.S. to continue to take prudent steps to defeat any future North Korean ICBM," Miller said in his speech Tuesday.
The Associated Press contributed to this report.