The United States Defence Secretary Chuck Hagel says he plans to bolster missile defences on the nation's west coast to counter the threat from North Korea.
He says the US will add 14 interceptors, which can shoot down missiles in flight, to 30 already in place in California and Alaska by 2017.
Mr Hagel cites a "series of irresponsible and reckless provocations" recently by North Korea, the BBC reports.
Pyongyang carried out a third nuclear test last month.
A statement in North Korean state media last month also threatened the US with a pre-emptive nuclear strike.
Europe plan shelved
But analysts say the regime is years away from producing a missile capable of carrying a nuclear warhead to the US.
"The US has missile defences to protect us from limited ICBM [Inter-Continental Ballistic Missile] attacks," Mr Hagel says.
"But North Korea in particular has recently made advances in its capabilities and has engaged in a series of irresponsible and reckless provocations."
The defence secretary says the US needs to "stay ahead of the threat".
North Korean soldiers shouting anti-US slogans at an undisclosed location North Korea has recently ramped up anti-US rhetoric
He said the additional 14 interceptors would be deployed to Fort Greely in Alaska at a cost of about $US1 illion.
As part of the strategy, the US will also deploy a radar-tracking station in Japan.
The Pentagon will shift some of the funding away from the missile defence programme it has been setting up in Europe.
Mr Hagel said US commitment remained "ironclad" to the European shield, and that missile batteries would be established in Poland and Romania by 2018.
But he said the another part of the plan had been shelved.
The Department of Defence principal under-secretary for policy James Miller later clarified that the final phase of the missile defence programme had been dropped.
"The prior plan had four phases. The third phase involved the deployment of interceptors in Poland. And we will continue with phases one through three," Mr Miller told reporters.
"In the fourth phase, in the previous plan, we would have added some additional type of interceptors - the so-called SM-3 IIB would have been added to the mix in Poland.
"We no longer intend to add them to the mix, but we'll continue to have the same number of deployed interceptors in Poland that will provide coverage for all of Nato in Europe," he added.
President George W Bush first proposed a defence shield in Europe, which had incensed Russia.
His successor Barack Obama rolled back on the plans, announcing a much smaller deployment.
Friday's announcement represents a further toning down of the plans.
The Pentagon says its top North Korea official will be visiting Russia and Germany next week.
The Alaska and California sites were built during the presidency of George W Bush as protection from a possible strike by North Korea.
Technical difficulties with the interceptors slowed their installation.
When asked about the "poor performance" of interceptors during recent trials, Mr Hagel say further tests willd be carried out this year.
"We have confidence in our system," he says, "and we certainly will not go forward with the addition of the 14 interceptors until we're sure we have the complete confidence we need."