WASHINGTON — The United States will deploy additional ballistic missile interceptors along the Pacific Coast to increase the Pentagon’s ability to blunt a potential attack from North Korea, in a clear response to recent tests of nuclear weapons technology and long-range missiles by the North.
The new deployment will increase the number of ground-based interceptors based in California and Alaska from 30 to 44.
While the limited missile-defense system does not offer a 100 percent guarantee of knocking down a North Korean attack, the weapons send a signal of credible deterrence to the North’s limited intercontinental ballistic missile arsenal.
The Navy also recently bolstered its deployment of ballistic missile defense warships in waters off the Korean Peninsula, although the vessels were sent as part of an exercise even before an increase in caustic language from the North.
As part of the Foal Eagle military exercise with South Korea, the Navy has four Arleigh Burke-class guided missile destroyers in the region.
Officials acknowledged that the ground-based interceptors had shown dubious capabilities in tests.
In announcing the deployments at the Pentagon on Friday, Defense Secretary Chuck Hagel cited North Korea’s recent test of nuclear technology and long-range missiles, including the development of a mobile missile, as well as its launching of a satellite that showed increasing range for the North’s arsenal.
“The United States stands firm against aggression,” Hagel said.
The new interceptors are scheduled to be deployed by 2017, at an estimated cost of just under $1 billion.
Officials acknowledged that the ground-based interceptors in Alaska and California had shown dubious capabilities in tests, and said the additional interceptors would be deployed only when they had proved their capability.
“We have confidence in our system,” Hagel said.
This week, the Pentagon’s undersecretary for policy, James N. Miller, foreshadowed the announcement in a speech to the Atlantic Council here, when he described efforts to improve early-warning radars and the command-and-control architecture of the missile-defense system based in California and Alaska.
“Our homeland ballistic missile-defense capabilities are intended in part to make it clear to both Iran and North Korea that if they develop ICBMs, they will not be able to threaten the United States,” Miller said, using the initials for intercontinental ballistic missiles. “Our missile defenses will defeat them.”
The interceptors in California and Alaska are to blunt a long-range missile threat from North Korea. The United States also deploys Patriot Advanced Capability batteries in South Korea for defense of targets there.
Japan is also developing its own layered missile-defense system, which includes Aegis warships and Patriot systems.
The United States deploys one advanced TPY-2 missile-defense tracking radar in Japan to enhance early warning across the region and toward the West Coast, and it has reached agreement to deploy a second.
Hagel cited three recent developments in North Korea that prompted the Obama administration to act, including a nuclear test in February deemed reckless by Washington and condemned by the United National Security Council.
Hagel also cited Pyongyang’s launch of a rocket in December that put a satellite into space and demonstrated mastery of some of the technologies needed to produce a long-range nuclear missile.
And he noted that last April the North Koreans put on public display a road-mobile intercontinental ballistic missile, the KN-08.
Admiral James Winnefeld Jr., vice chairman of the Joint Chiefs of Staff, said that missile is believed to be capable of reaching US territory. Winnefeld appeared with Hagel at Friday’s news conference.
Although not mentioned by Hagel, North Korea raised tensions further by threatening last Thursday to preemptively attack the United States. Among its recent declarations, North Korea has said it will no longer recognize the armistice that ended the 1950-53 Korean War, though it has made such remarks before.
In a separate development Friday, North Korea said hackers from the United States and its allies were working to shut down its websites, the country’s main tool of spreading propaganda abroad.
Until now, the complaint came from the other direction, with South Korean officials suspecting that North Korea was behind a recent series of hacking attacks on South Korean and US websites.
After North Korea’s recent threats to retaliate against UN sanctions, South Korea warned of possible North Korean efforts to disrupt the Internet in the South, one of the most wired countries in the world.
These accusations, although denied by the opposing sides, showed how inter-Korean tensions are increasingly spreading into cyberspace.
“It is nobody’s secret that the US and South Korean puppet regime are massively bolstering up cyberforces in a bid to intensify the subversive activities and sabotages against the DPRK,’’ the North’s Korean Central News Agency said, using the acronym of the country’s official name, Democratic People’s Republic of Korea. ‘‘They are seriously mistaken if they think they can quell the DPRK’s voices of justice through such base acts.’’
North Korea’s often strident rhetoric has escalated to a feverish new pitch in recent weeks, complete with a threat to launch a ‘‘preemptive nuclear attack’’ at the United States and South Korea after the allies started joint military drills on March 1, followed by new UN sanctions for the North’s Feb. 12 nuclear test.
North Korea did not elaborate on what it called ‘‘intensive and persistent virus attacks’’ on its Internet servers. But Russia’s Itar-Tass news agency said a ‘‘powerful hacker attack’’ from abroad had brought down Internet servers inside the North. Nevertheless, the North’s two main channels of government statements and propaganda — the websites of the Rodong Sinmun newspaper and the Korean Central News Agency — operated normally Friday.