A plan by the United States to possibly abandon the final phase of its European missile defence system could revive arms-control talks with Russia.
As part of plans announced on Friday to deploy more anti-missile batteries in Alaska to thwart potential strikes from North Korea, the United States intends to "restructure" its missile defence program in Europe, an administration official said.
US President Barack Obama's plan for Europe had envisaged SM-3 interceptors on land and sea and upgrades over four stages.
The final phase of the missile-killing interceptor, known as SM-3 IIB, was due to be deployed within about 10 years in Poland and possibly Romania, with a more powerful booster rocket and other advanced hardware.
But the final phase "is being restructured due to congressional funding cuts and changing technology", an administration official said.
"The goal is to research what alternative there could be to the original SM-3 IIB plan," the official added.
The decision could cause dismay in Poland and Romania but will likely be welcomed in Moscow, as Russian officials had seen the more sophisticated interceptor as aimed at its missile arsenal and undercutting its nuclear deterrent.
The issue had become an obstacle to progress on further arms control agreements and analysts say scrapping the final block of interceptors could create momentum for fresh negotiations.
But the administration official insisted the decision was based on financial and technical considerations and not meant as a signal to Moscow.
"This has never been about Russia but about missile defence for our allies in Europe against threats from Iran," the official said.
A year ago, Obama told Russian President Dmitry Medvedev that he would have "more flexibility" to negotiate with Moscow after America's November elections, in a remark picked up by a nearby microphone.
Obama's comment sparked sharp criticism from Republicans in Congress, and the administration's decision to move away from the final phase of the missile defence blueprint in Europe will ignite fresh anger among lawmakers.
But apart from the contentious politics around the issue, the science behind the planned final phase of the SM-3 interceptor has come into question.
The Defence Science Board, a panel of civilian experts, said in 2011 that the concept of the more advanced SM-3 - to intercept missiles at an early stage before the deployment of warheads - would require "Herculean effort and is not realistically achievable, even under the most optimistic set of deployment, sensor capability, and missile technology assumptions".
And a report in September by a National Academy of Sciences committee called for dropping the fourth phase of the European missile defence plan in favour of a new interceptor site on the US East Coast.
Dropping the final phase of the SM-3 interceptor also would help offset the US$1 billion cost of deploying an additional 14 interceptors to Alaska to counter North Korea's potential long-range missile threat, which was announced on Friday by Defence Secretary Chuck Hagel.
Obama administration officials hope to forge another deal on nuclear arms reductions after the agreement struck with Moscow in 2010, the first accord in two decades. It limited each side to 700 deployed long-range missiles and heavy bombers.