Nato's chief has discounted concerns in Moscow that US proposals to build a missile defence system in Europe could lead to a new arms race with Russia.
Russia says there should be a common approach to threats
Secretary General Jaap de Hoop Scheffer said the system would not affect strategic balance or threaten Russia.
Moscow strongly opposes the system. Washington says it is needed to protect the US and Europe from possible attack by hostile nations such as Iran.
The US wants parts of the shield to be sited in the Czech Republic and Poland.
The plan is to base 10 interceptor missiles in Poland with an associated radar in the Czech Republic.
"Ten interceptors will not, cannot and will not affect the strategic balance and 10 interceptors can also not pose a threat to Russia," Mr de Hoop Scheffer said after talks at Nato headquarters in Brussels.
'That extra mile'
Due to its location, the proposed US missile defence system will not protect all Nato member states. Turkey and parts of Greece will not be covered.
The secretary general said there was a desire among the 26-nation alliance that any US system should be able to work alongside any additional Nato defensive system to extend coverage to these two member states.
Earlier, alliance members agreed that "there is a threat to Europe of missiles" and that their security must be "indivisible".
"There were no critical comments, but there was the strong belief that we should pursue the indivisibility of security and maintain maximum transparency," said Nato spokesman James Appathurai.
The BBC's diplomatic correspondent Jonathan Marcus says winning the Russians around, or going that extra mile to try and embrace Moscow's concerns, may be a vital condition if harmony within Nato is to be maintained.
US officials said a number of confidence-building proposals had been put to the Russians and that discussions would continue.
The Russian ambassador, Konstantin Totsky, said that if there was a common missile threat as the US says, then there should be a common security approach to meet it.
Mr Totsky hinted that Russia's response would be to deploy new systems of its own - what the Russian diplomat described as an asymmetric response that would be cheaper than the US programme, says our diplomatic correspondent.