US President Barack Obama has shelved plans for controversial bases in Poland and the Czech Republic in a major overhaul of missile defence in Europe.
The bases are to be scrapped after a review of the threat from Iran.
Mr Obama said there would be a “proven, cost-effective” system using land- and sea-based interceptors against Iran’s short- and medium-range missile threat.
Russia, which saw the old shield as a threat, initially welcomed the news but there has been criticism in the US.
The US signed a deal in August 2008 with Poland to site 10 interceptors at a base near the Baltic Sea, and with the Czech Republic to build a radar station on its territory.
The US had said the missile shield would be fully operational by 2012.
But President Obama this year ordered a review of the defence system, which was strongly backed by his predecessor George W Bush.
‘Stronger and smarter’
On Thursday, President Obama said in a live TV address that the change was needed to “deploy a defence system that best responds to the threats we face”.
He said a review had shown the need to switch strategy to defending against the short- and medium-range missiles that Iran could use to target Europe.
Twice Mr Obama referred to the need for a system that was “proven and cost effective”.
He said the new approach would provide “a stronger, smarter and swifter defence” of US and allied forces in Europe.
Mr Obama said he had spoken to both the Czech Republic and Poland and stressed his commitments to their defence.
But he said again that Russia’s concerns about the old system were “entirely unfounded”.
White House spokesman Robert Gibbs later stressed the overhaul was “not about Russia”.
Although the White House said the US “no longer planned to move forward” with the old shield scheme for Poland and the Czech Republic, Defence Secretary Robert Gates stressed the US was not abandoning missile defence of Europe.
He said negotiations were under way with both nations about deploying upgraded SM-3 interceptors from 2015.
The first phase of the new strategy, he said, would be to deploy “current and proven missile defence systems in the next two years”, including the sea-based Aegis and the current SM-3.
The overhaul marks a major US foreign policy shift but it has already drawn some criticism.
John Bolton, who was undersecretary of state for arms control and international security under President Bush, said the move was “unambiguously a bad decision”.
He said: “This gives away an important defensive mechanism against threats from countries like Iran and other rogue states, not only for the US but for Europe as well.
“It is a concession to the Russians with absolutely nothing in return.”
Iran says its missile development programme is solely for scientific, surveillance or defensive purposes, but there are concerns in the West and among Iran’s neighbours that the rockets could be used to carry nuclear weapons.
As part of long-running efforts to tackle the issue, Iran will hold talks on its nuclear programme on 1 October with the UK, China, France, Russia and the US – the five permanent UN Security Council members – and Germany.
‘Real work’
Russia had seen the old US missile plan as a direct threat, despite US assurances that it was aimed at “rogue” states, such as Iran.
When news of the overhaul broke, Russia’s ambassador to Nato, Dmitry Rogozin, said it was “a breakthrough” for US-Russian relations.
“This means we’re getting rid of one of those niggling problems which prevented us from doing the real work,” he said.
The two countries are currently in talks about reducing their nuclear weapons stockpiles, and the US move could influence Russia to be more co-operative, correspondents say.
Nato Secretary-General Anders Fogh Rasmussen said the US move was “a positive step”, Associated Press reported.