NATO was set Thursday to agree a major boost to its defences in eastern Europe including six bases and a spearhead force of 5,000 troops in response to what it called Russian aggression in Ukraine.
Secretary General Jens Stoltenberg insisted that the moves likely to be approved by defence ministers meeting in Brussels were purely defensive, but the increased presence on Russia's borders is likely to rile Moscow.
With Eastern European states concerned by the worst tensions with Russia since the Cold war, the bases will be in the alliance's three Baltic states -- Estonia, Latvia and Lithuania -- plus Poland, Romania and Bulgaria.
"This is something we do as a response to the aggressive actions we have seen from Russia, violating international law and annexing Crimea," Stoltenberg told reporters as he arrived at the 28-nation group's headquarters.
"It is a response to what we are seeing from Russia over a period of time, and it is in full accordance with our international obligations," the former Norwegian prime minister said.
As the ministers met, US Secretary of State John Kerry arrived in Ukraine for talks expected to touch on Kiev's hopes that the Washington will supply weapons.
NATO leaders agreed to step up the alliance's eastern defences at a summit in Wales in September, amid concerns about Russia's actions in Ukraine and a increase in Russian military actitivity on NATO's borders.
Stoltenberg said the NATO measures were also motivated by new threats from Islamist militants in North Africa and the Middle East who are fuelling violence within Europe.
The NATO defence ministers are expected to agree on a so-called "spearhead" force of around 5,000 troops which will be able to deploy anywhere within a "few days," Stoltenberg said.
They are also to finalise the list of the countries taking part in the force, which a NATO official said would hopefully be operational by 2016.
- Six 'command and control' bases -
The ministers will further increase a wider NATO response force, which would take weeks or months to deploy in a crisis, from 13,000 to 30,000 troops, he said.
NATO will also decide on six "command and control" units in Eastern European nations to ensure that the new force could hit the ground running.
The multinational headquarters for the command and control centres will be in Szczecin, Poland, which will also be boosted, he said.
The Baltic states used to be part of the Soviet Union while Poland, Romania and Bulgaria were all part of the Warsaw Pact, the Moscow-led military alliance in the Cold War.
"They will plan, organise exercises and they will be a key for connecting national forces with NATO reinforcements," the alliance chief said.
The question of whether the West could arm the Kiev government in its battle against Russian-backed rebels will hang over the meeting but is unlikely to be discussed, sources said.
The NATO chief said he would meet later this week on the sidelines of the Munich security conference with US Vice President Joe Biden, Ukrainian President Petro Poroshenko and Russia Foreign Minister Sergei Lavrov.
He said his talks with Lavrov are part of keeping political channels open with Russia after the alliance ended "practical cooperation" with Moscow over the Ukraine crisis.
The Western allies are still seeking a diplomatic solution to the crisis in Ukraine, where government forces have been fighting pro-Moscow rebels since April in a conflict that has claimed nearly 5,400 lives.
"We are calling on Russia to stop support for the separatists and to respect the Minsk (truce) agreement and to use all its influence on the separatists to respect the ceasefire," he said, referring to a largely ignored peace deal signed in September.