(CNN) - The United States will deploy additional ground-based missile interceptors as part of efforts to enhance the nation's ability to defend itself from attack by North Korea or Iran, Defense Secretary Chuck Hagel announced Friday.
Still relatively new in his post, the Pentagon chief told reporters that 14 additional interceptors would bring the total to 44. He said the expansion should be completed by 2017.
Part of the move would involve reopening a missile field at Fort Greely, Alaska, Hagel said.
"The reason that we are doing what we are doing and the reason we are advancing our program here for homeland security is to not take any chances, is to stay ahead of the threat and to assure any contingency," Hagel said.
The move comes after North Korea recently threatened a pre-emptive nuclear attack on South Korea and the United States in response to stepped-up U.N. Security Council sanctions over its latest nuclear test.
North Korea also said last week it was nullifying the joint declaration on the de-nuclearization of the Korean Peninsula. One of the country's top generals, according to published reports, claims Pyongyang has nuclear-tipped intercontinental ballistic missiles that are ready to be fired.
In addition, Iran is believed to be continuing its efforts to develop nuclear weapon capability.
Military and White House officials have said the United States can defend against any such threat, and President Barack Obama said in an interview with ABC News this week that he does not think North Korea can make good on the threat.
"They probably can't but we don't like margin of error," Obama said.
Hagel said Friday that the U.S. missile defense systems in place provide protection from "limited ICBM attacks," but added that "North Korea, in particular, has recently made advances in its capabilities and has engaged in a series of irresponsible and reckless provocations."
He acknowledged a problem with the guidance system of missile interceptors and said further testing would occur this year.
"We certainly will not go forward with the additional 14 interceptors until we are sure that we have the complete confidence that we will need," Hagel said. "But the American people should be assured that our interceptors are effective."
He also announced the military will work with Japan to increase radar capability to improve early warning and tracking of any missile launched from North Korea.
In 2011, the Pentagon mothballed Missile Field 1 in Alaska, acting on direction from the Obama administration. Instead of permanently decommissioning it, the Defense Missile Agency placed it in a non-operational state.
Pentagon officials testified at a budget hearing at the time that hardening and reactivating the six silos in Missile Field 1 would take two years and cost approximately $200 million. Pentagon officials testified then that "there are no current threats dictating the need, nor plans to reactivate MF-1 in the future."
Republican congressional sources told CNN that they argued against the move.
"North Korea was doing all sorts of things we couldn't talk about publicly back then," said one GOP congressional official who is privy to intelligence briefings. "The intelligence did not change. This is right where we expected North Korea to be. It takes about two years to order and take delivery of a new interceptor. That's why you have to be ahead of the threat."
In his State of the Union address last month, Obama said the United States would "stand by our allies, strengthen our own missile defense and lead the world in taking firm action in response to these threats."
Last week, Undersecretary of Defense for Policy James Miller told the Atlantic Council that "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" intercontinental ballistic missile.