In an effort to counter Russian aggression, Nato leaders approved plans yesterday to set up a rapid reaction force in eastern Europe comprising several thousand troops.
Nato Secretary General Anders Fogh Rasmussen said the new unit would send a clear message to potential aggressors.
"Should you even think of attacking one ally, you will be facing the whole alliance," he declared as a two-day Nato summit in south Wales drew to a close.
The agreement on the rapid response force was the cornerstone of discussions at the summit on how to combat Russia's provocations in Ukraine.
While Ukraine is not part of the Nato alliance, Russia's actions have prompted fears among member countries in central and eastern Europe that the Kremlin could seek to make gains within their borders as well. The force will include land, air and sea assets, and is likely to number about 5,000 troops.
The announcement came as Ukrainian President Petro Poroshenko voiced "careful optimism" that talks with pro-Russian separatists in the Belarusian capital, Minsk, would set the course for a ceasefire after more than five months of fighting.
But Nato officials said it was too early to tell if Russian President Vladimir Putin was genuine about his proposals for peace.
The conflict has killed more than 2,500 people. Ukraine, the US and Europe say Putin is backing the insurgency in Donetsk and Luhansk with financing, weapons and manpower. Russia denies any involvement.
The talks in Minsk brought together representatives of Ukraine, the separatists, Russia and the Organisation for Security and Cooperation in Europe, which would police any cessation of hostilities.
As well as agreeing on a truce, the parties must resolve differences over the legal status of Donetsk and Luhansk as well as Ukraine's plans to join Nato.
The summit and European Union moves towards more sanctions on Russia formed the backdrop for the diplomacy. The US has been working on a new round of sanctions "for some time", says the White House.
Associated Press, Bloomberg