Poland scrambled fighter jets and an early warning aircraft, and put its ground air defenses and radar systems on "the highest state" of alert.

Russian jets violated NATO airspace over Lithuania for 18 seconds during suspected refueling exercise. Nation's president calls it a breach of international law amid tensions.

For the first time, NATO allowed journalists to witness its annual nuclear exercise, a once-secret event that now serves as both a show of transparency and a message of deterrence toward Russia.

The new French submarine-launched ballistic missiles provide enhanced range, accuracy and the ability to penetrate defenses.

The missile, named the Mark 1, was developed last year to shoot down enemy drones at short range and is awaiting its debut on the global weapons market. Mr. Salm, chief executive of its manufacturer, Frankenburg Technologies, hopes it will fill a gap in Europe’s air defenses against Russia. “Clearly, we are unprepared,” he said.

Authorities said the balloons are likely for smuggling, but blamed Belarus' leader, Alexander Lukashenko, for letting them float over.

The Russian Il-20 did not file a flight plan for its "reconnaissance mission" in international airspace, Poland's military has said.