NATO foreign ministers met Thursday to finalise the alliance's biggest military build-up since the end of the Cold War to counter what they see as a more aggressive and unpredictable Russia.
At a Warsaw summit in July, NATO leaders will sign-off on the revamp which puts more troops into eastern European member states as part of a "deter and dialogue" strategy, meant to reassure allies they will not be left in the lurch in any repeat of the Ukraine crisis.
NATO chief Jens Stoltenberg said the two-day meeting will address "all the important issues" to prepare for a "landmark" summit in Poland.
"We will discuss how NATO can do more to project stability ... and at the same time address how NATO can continue to adapt to a more assertive Russia to find the right balance between defence and dialogue," he told reporters.
Helping struggling countries help themselves rather than have NATO always take the lead was more effective, he said, citing growing challenges to the south, from conflict in Syria and Iraq to instability across North Africa.
The fear is that terrorist groups such as Islamic State (IS) can exploit the turmoil.
In November, IS attacks in Paris left 130 dead and in March jihadis killed 32 in Brussels -- home to NATO HQ, the European Union and a host of diplomatic and corporate offices.
The EU meanwhile is grappling with the worst migrant crisis since the end of World War II, and the bloc wants increased cooperation with NATO to tackle the problem, notably in bolstering the UN-backed government in Libya where IS has recently gained ground.
EU foreign affairs head Federica Mogherini will join the NATO ministers on Friday.
Of the 28 NATO member states, 22 also belong to the EU where Mogherini is overseeing a review of its global security strategy.
US ambassador to NATO Douglas Lute said Wednesday foreign ministers would have a "very sober discussion on dealing with Russia... which essentially has thrown out the rulebook."
"This is not the predictable partner we thought we had," Lute added.
NATO will sign later Thursday an accession accord with Montenegro, another bone of contention with Russia over the future of the Balkans, home to historic Slav allies and a key strategic interest.
Georgia, which fought a brief 2008 war with Russia, is also seeking membership but when asked Thursday if Tbilisi could expect similar progress, Stoltenberg notably stopped short of commenting directly on its accession prospects.
Instead, he stressed NATO would continue to boost cooperation, including military training, with the former Soviet republic.
Russia's intervention in Ukraine and its 2014 annexation of Crimea stung NATO into action after years of complacency and defence cuts following the fall of the Soviet Union.
Moscow however says NATO is encroaching on its borders, while Washington builds a European missile defence shield which undercuts Russia's nuclear deterrent.
Mutual suspicion runs deep -- former NATO deputy supreme commander Richard Shirreff warned Wednesday the West could find itself at war with Russia next year unless it boosted its defences.
Stoltenberg had cautioned Wednesday against a new arms race, stressing the alliance upgrade was purely "defensive, proportionate and in line with our international obligations."
NATO wanted dialogue with Russia to ease tensions and avoid potentially dangerous incidents getting out of control, he said.
NATO suspended all practical cooperation with Russia over Ukraine but left a channel of communication open through what is known as the NATO-Russia Council (NRC).
Stoltenberg convened the first NRC since June 2014 last month, which he said produced a "frank" but also "useful" exchange.
NATO diplomatic sources said some member states wanted another NRC before the Warsaw summit, as at least a gesture of good faith, but others are reluctant, seeing no reason to cut Russia any slack.
"I think there will be a meeting... a number of allies want it quite badly and the rest of us think it is not worth fighting about," one source said, downplaying the NRC's importance.