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.

The incursion of a significant number of Russian drones into Poland is a dramatic and unsettling escalation of the war in Ukraine.

The new initiative, known as Eastern Sentry, follows the incursion of Russian drones in Polish airspace on Wednesday.

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.

A police officer stands below as firefighters work on the destroyed roof of a house, after Russian drones violated Polish airspace during an attack on Ukraine, with some being shot down by Poland with the backing from its NATO allies,