NATO says it's bulking up its defensive posture on its eastern flank bordering Belarus, Russia and Ukraine with new equipment.

European leaders accused Russia on Thursday of a deliberate incursion by sending drones to invade Polish airspace, and said they saw the provocation as a test — both for the Kremlin and for Europe — of NATO’s readiness to defend its territory.

With Russia’s invasion of Ukraine in its fourth year, and the US wavering in its commitment to Western European security, there’s speculation that Russian President Vladimir Putin is testing NATO’s collective security arrangements.

Military capability of Western alliance remains 'formidable' despite questions around untested 'mutual assistance' agreement as Trump pivots away from Europe

Alarms bells sounded this week in Europe after NATO jets scrambled to intercept an unprecedented Russian drone incursion in Poland. Now there is fresh unease on NATO’s eastern flank, as Russia and Belarus kick off major military drills to test the readiness of their armed forces.

Polish Prime Minister Donald Tusk told parliament it was "the closest we have been to open conflict since World War Two."

Kyiv fears that Europe will react to Russia’s drone incursion into Poland by keeping its air defenses to itself instead of helping embattled Ukraine.

President Donald Trump reacted Wednesday with a degree of bemusement toward Russia’s drone incursion into Poland, a NATO member that Trump has previously vowed to defend amid heightened tensions with Moscow.