By Andrius Sytas and Marek Strzelecki NERIS SUBSTATION, Lithuania (Reuters) -Four NATO and European Union countries bordering Russia plan to build concrete bunkers and anti-drone nets at vital energy facilities under a plan to protect their power grids following Russian drone incursions.

Denmark's Defense Ministry has reported again observing drones at several military locations overnight as NATO is on high alert over recent Russian military actions in Europe.

NATO scrambles to counter Russian drones and airspace violations. Poland vows shootdowns, but allies fear escalation as Europe shoulders defence burden.

NATO said the new measures include surveillance systems and a frigate, expanding the mission launched to protect Baltic Sea infrastructure.

A Canberra-made laser is about to become NATO's newest frontline defence against enemy drones, in a deal experts say could transform the future of warfare.

Denmark’s defense ministry said that it had “several capacities deployed” after drone sightings from Saturday into Sunday night.

Denmark reported the latest in a series of drone sightings on Saturday, with the most recent incident occurring near military installations.

Russian Foreign Minister Sergey Lavrov warned, 'Any aggression against my country will be met with a decisive response.'