By Nick Thorpe
BBC News, Romania
It would be a nonsense to say that a defensive system is directed against a certain country, or a certain group of countries. In my view there is no danger of misinterpretation.
Bogdan Aurescu, state secretary for strategic affairs at the Romanian foreign ministry
We are again becoming witnesses to a hasty anti-missile arrangement for Europe when the fragile architecture of European security essentially becomes hostage to imaginary missile threats that are defined unilaterally.
Andrei Nesterenko, spokesman for the Russian foreign ministry
When George W Bush was US president, his missile defence plan proposed interceptor missiles in Poland, coupled with a new radar in the Czech Republic.
The land-based missiles would be similar to the one above
President Barack Obama won rare praise from Moscow for scrapping that plan, which the Russians suspected was aimed against them.
But the thaw did not last long. Last September, Washington announced what it called the Phased Adaptive Approach (PAA) to missile defence.
This new system would start by stationing missile defence assets in south-east Europe, and slowly spread its web to the centre and finally the north.
The US defence department, in its Ballistic Missile Defense Review, reckons the ballistic missile threat "is increasing both quantitatively and qualitatively, and is likely to continue to do so over the next decade".
It points particularly to missile programmes in North Korea and Iran.
As part of the PAA, Romania has announced that it will accept up to 24 land-based interceptor missiles. Talks with the US on the details will begin soon.
And the Bulgarian government has offered to play host to the radar component which complements the missiles.
Russia has again expressed concern, and missile defence is one of the points of contention that held up Russian-US talks to replace the 1991 Start arms control treaty - before the two sides said they had agreed a new deal late last month.
But Romania insists the deal will make the region more secure. Bogdan Aurescu, the chief Romanian negotiator in the coming talks with the US on the details of Romanian participation, says it will lead to "increased security for Romania, and more security for the Black Sea region as a whole, not only for Romania and its allies".
Regarding Russian concerns, he says: "We also have to focus our efforts and energy to avoid suspicion between us, and to clarify our intentions.
"That's why a process of transparent consultation and discussion is always needed."
The introduction of the interceptors and radar clearly represents a shift in the balance of power in south-east Europe, following 2008's Russia-Georgia conflict, and Ukraine's new president's offer to extend Russia's lease on its naval base at Sevastopol in the Crimea.
"The Black Sea region... will be a very interesting hub, in terms of the arms race and everything we can can see developing on the eastern border of Nato," says Radu Tudor, a defence analyst in Bucharest.
Romania says there are several differences between the new US plan and the earlier, Czech-Polish version.
US concerns focus on Iranian testing, which Iran has said is for research
It will cover a wider area, it will be ready earlier - in 2015 for the south-east European segment - and the SM-3 missiles can incorporate new technology, as it is developed.
No sites have yet been decided, but two almost certainly under consideration are the Mihail Kogalniceanu airbase near the Black Sea coast, and a military airfield near Cluj in Transylvania.
The Romanian authorities expect little public opposition.
All major parties in the Romanian parliament support it, and the plan has already sailed through its first committee hearing in the Senate.
Some politicians hope it will also help extract a long-standing thorn in Romanian-US relations - the tough visa regime Romanian visitors to the US still face.
"We don't see that it's correct or fair towards Romanian citizens," says Titus Corlatean, head of the Foreign Affairs Committee of the Senate, "considering some European countries that do not contribute to the same extent as Romania to the American and international effort, already enjoy a visa waiver system".