Estonia's defence minister said a Russian plane had violated its airspace over the weekend, as all three Baltic states and Poland expressed concern over unprecedented Russian military activity in the region.
Russia's actions in Ukraine, including its March annexation of the Crimean peninsula, have spooked neighbouring Poland and Baltic trio Estonia, Latvia and Lithuania -- all new NATO members formerly dominated by Moscow.
"We've seen large-scale movements in the air," Estonian Defence Minister Sven Mikser told reporters on Friday after two days of talks in Latvia with his Polish and Baltic counterparts.
"We've seen long-range strategic bombers flying, which are not usual visitors in our region. Those moves are unnecessarily provocative.
"We had at least one incident of our sovereign airspace violation also during the weekend," he added, without elaborating.
Poland's defence minister Tomasz Siemoniak said Thursday that "for a few days now" there had been "unprecedented Russian activity from its Baltic fleet to flights over the Baltic sea".
The Baltic states echoed the statement Friday, while insisting they refused to be intimidated.
"Any aggressive move by any external power against a NATO ally will be met by an immediate and decisive response," Mikser said.
"There's no doubt that NATO collectively is vastly superior to Russia when it comes to conventional military power."
NATO said more than 30 Russian aircraft were intercepted in international space over the Baltic Sea and off the coast of Norway on Monday alone.