MILAN/LONDON — Suspected Russia-backed hackers have launched exploratory cyber attacks against the energy networks of the Baltic states, sources said, raising security concerns inside the West’s main military alliance, NATO.

Lithuania, Latvia and Estonia, all members of NATO and the European Union, are on the political front line of tensions between the West and Moscow. The Baltics are locked into Russia’s power network but plan to synchronize their grids with the EU.

Interviews with more than a dozen law-enforcement and private investigators, insiders and utility officials show hackers have quietly made incursions into Baltic networks over the past two years, in parallel with more serious attacks in Ukraine that plunged swathes of that country into darkness.

They say Russian state organizations are suspected of being behind the campaigns.

Reuters could not independently verify the sources’ allegations.