Germany's Angela Merkel promised the Baltic states on Monday that NATO would defend them, although it would not send permanent combat troops but would increase manoeuvres in the region, Reuters reports.
Latvia, Estonia and Lithuania - former Soviet republics with their own Russian-speaking minorities - are increasingly anxious that the conflict in Ukraine and Russia's annexation of Crimea could herald destabilisation in their own region by Moscow.
The Baltic states have asked for an increased NATO presence to reinforce Article 5 of the alliance's constitution, which states that an attack on one of its members is an act of aggression against all, obliging them to react.
"I want to stress that ... Article 5 of the NATO contract - the duty to provide mutual support - is not something which just exists on paper, but is also something which must be filled with life," said Merkel on a visit to the Latvian capital, Riga.
NATO's top commander said over the weekend that the alliance would respond militarily if Russia tried to infiltrate troops into a NATO country.
Merkel told a joint news conference with Latvian Prime Minister Laimdota Straujuma that Germany would start "air policing" flights in Latvia from Aug. 20.
"But we must also now supplement this with further exercises and manoeuvres, so that we can react swiftly and without hesitation," she said. "Everything must be done so that we have the infrastructure in the Baltic states to react quickly."
Merkel said NATO leaders would discuss this at their summit in Cardiff on Sept. 4-5 and she expected them to reach a unified position.
"We won't have a permanent stationing of combat troops but we will boost our participation in other ways ... we will do what it takes to guarantee that, should Latvia come into difficulties, NATO will be able to help straight away," she added.
Latvian premier Straujuma said Russia's actions in Ukraine had "fundamentally changed the security environment in Europe".
"Trust has been lost. We all have to adjust ourselves to the new conditions and we must give a clear response," she said.