Nato is not seeking confrontation with Russia and does not want another Cold War, Secretary-General Jens Stoltenberg has told the BBC.
The planned deployment of 4,000 extra troops to eastern Europe aims to prevent, not provoke conflict, he said.
Despite current tensions, the military alliance does not see Russia as a threat, he added.
Relations between the west and Russia are at their lowest point since the Cold War.
The US and European Union imposed sanctions on Russia following its annexation of Ukraine's Crimean peninsula in 2014.
The war in Syria has also been a flashpoint for tensions, with key Western powers accusing Russia of war crimes in its bombardment of opposition-held areas in support of the Syrian government.
Why is Nato deploying more troops? - BBC defence correspondent Jonathan Marcus explains
Russia is in many ways a weak country. Its leadership has a strong sense of encirclement - a view that the West is only eager to do it down - and, rightly or wrongly, this is driving Mr Putin's more assertive approach.
That is what is making Nato allies like the three Baltic Republics and Poland so worried. That is why countries like Romania and Bulgaria worry about Russia's behaviour in the Black Sea region.
And that is why Nato has sought to provide visible and highly symbolic reinforcements to its northern and south-eastern flanks.
But Nato has to square a circle here. Despite Mr Putin's barbs, there is no great enthusiasm for a new conventional arms race.
Russian President Vladimir Putin has rejected those allegations, and says the idea that Russia has aggressive military designs in Europe as "ridiculous".
Multi-national Nato battalions made up of 1,000 troops each will be deployed to Poland, Estonia, Latvia, Lithuania early next year.
They will be led by the US, Britain, Canada and Germany.
But rather than seeking to confront Russia, Nato continues "to strive for a more co-operative and constructive relationship", Mr Stoltenberg said, interviewed during a Nato meeting in Brussels.
"But we have to do that based on collective defence - deterrence."
While Nato did not see any imminent threat from Russia, it was responding to its actions in Ukraine, he said, as well as what he called the use of nuclear rhetoric to intimidate European nations.
Nato says it believes Russia has about 330,000 troops stationed near its western border.
Earlier this week, plans for Russian warships to dock at a Spanish port were cancelled after Nato allies voiced concern that they could be used to bomb civilians in Syria.