NATO defence ministers have agreed to bolster protection in eastern Europe after the Ukraine crisis, but have insisted they are acting within the limits of a key post-Cold War treaty with Moscow.
NATO head Anders Fogh Rasmussen said ministers had agreed to develop a "readiness action plan... to respond to the changed security environment" created by the escalating conflict in Ukraine.
This will include measures such as pre-positioning supplies and equipment in member states and stepping up work to improve military capabilities to help NATO speed up its reaction time to any threat.
"We agreed that we will continue to reinforce NATO's collective defence with more air and sea patrols and more exercises and training, from the Baltic Sea to the Black Sea and the Mediterranean," Rasmussen said.
"I welcome the decision by Denmark, Germany and Poland to start work in order to raise the readiness of Multinational Corps North-East, based in the city Scezcin of Poland. This will strengthen our ability to address future threats and challenges in the region and it is a significant contribution to our collective defence."
The plan will go to NATO leaders at their September summit in Britain for approval.
Rasmussen also welcomed US President Barack Obama's announcement of a $1bn US security plan for eastern Europe aimed at reassuring NATO allies, who have been increasingly concerned by Russian actions.
'Breach' of treaty
Latvia, Lithuania and Romania have also announced plans to increase defence spending in response to the Ukraine crisis and Poland also proposed to slightly boost its military budget.
The decision comes after Moscow's annexation of Crimea and support for pro-Russian separatists in the east of Ukraine has plunged East-West relations to their worst point since the end of the Cold War.
Russia's intervention in Ukraine and its annexation of Crimea mean it "is in blatant breach of the 1997 Founding Act," Rasmussen said.
The 1997 NATO-Russia Founding Act formalised post-Cold War borders in Europe and crucially said neither the West, led by the United States, nor Russia would deploy forces or arms in the newly-freed east European countries
in a threatening manner.
Both sides also agreed that neither should treat the other as an "adversary," aiming to reduce the risk of future conflict.
Russia's ambassador to NATO, Alexander Grush, said on Monday that NATO's temporary deployment of additional alliance planes and troops in member states such as Poland and the Baltic countries amounted to a breach of the treaty.
Some NATO member states, especially in central and eastern Europe, have expressed concern and surprise at Russia's ability to mass 40,000 troops on the border with Ukraine very quickly and keep them there, ready for action, for some time.
Rasmussen said NATO had to take necessary measures for "as long as necessary" to counter a new threat.
He pointed out that Russia had increased defence spending by 50 percent over the last five years, while the allies have cut theirs by a fifth.