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.

WOHYN, Poland (AP) — Multiple Russian drones crossed into Poland in what European officials described Wednesday as a deliberate provocation, causing NATO to send fighter jets to shoot them down. A NATO spokesman said it was the first time the alliance confronted a potential threat in its airspace.

General Wiesław Kukuła, Chief of the General Staff of the Polish Armed Forces, has confirmed that the Polish side received information from Belarus about drones flying in its direction.

According to Muraveiko, during the night of Russia’s drone strikes on Ukraine, Belarusian air defense reportedly “tracked drones that went off course due to electronic warfare systems.” He added that some of the drones were allegedly shot down over Belarusian territory.

France said Friday it’s deploying fighter jets to Poland and the UK announced fresh sanctions targeting Russia’s oil revenues and war machine as Europe’s first, measured steps to Russia’s drone incursion into Poland aimed to send a signal to Moscow that any further aggression won’t go unchecked.