Brussels - Nato foreign ministers on Thursday were finalising 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.Nato chief Jens Stoltenberg said the two-day meeting would address "all the important issues" to prepare for a "landmark" summit in Poland in July.There, Nato leaders will formally endorse 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."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," Stoltenberg told reporters.While the focus has been on the eastern flank, there are also growing challenges to the south, with conflict in Syria and Iraq, and instability across North Africa.But rather than Nato taking a leading role there, Stoltenberg said it was better for the alliance to help struggling countries help themselves to cope with terrorist threats such as Islamic State (ISIS).In March, ISIS jihadis killed 32 people 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 ISIS has recently gained ground.Mutual suspicionsRussia'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 says Nato's response is just a cover for encroaching on its borders, while Washington builds a European missile defence shield which undercuts Russia's nuclear deterrent."I think you have to remember where this started," said a senior US official."Nato took these measures because Russia chose to invade and occupy Crimea and then move into eastern Ukraine. The concern ... was to ensure that this was not the beginning of a broader move that might threaten Nato territory."In another move likely to infuriate Moscow, Nato signed an accession accord with the tiny Balkan state of Montenegro on Thursday.Prime Minister Milo Djukanovic said Nato membership was a major step forward for his country "and will help bring about stability in the region and beyond".Among other states of the former Yugoslavia, Croatia and Slovenia have joined NATO to Russia's anger over the future of the Balkans, a key strategic interest and home to historic Slav allies.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 co-operation, including military training, with the former Soviet republic.Avoid new arms race Stoltenberg had cautioned on 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, 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.