Europe’s eastern borders were already on high alert after NATO forces shot down 19 Russian drones that invaded Poland’s airspace last Wednesday.

On Saturday, two Romanian F-16 fighter jets spotted a Russian drone over Romanian territory while doing a scouting exercise to monitor Russian airstrikes across the border in Ukraine.

Romania’s foreign minister slammed the incursion as “unacceptable and reckless.” No damage or injuries were reported, Romania’s defense ministry said in a statement.

In the previous Russian incursion into Poland, five drones had been on a direct flight toward a NATO base before being intercepted by Dutch Lockheed Martin F-35 fighter jets.

The incursion in Poland left no damage. But the incident exposed the transatlantic alliance’s poor planning for handling drones, which have emerged as a central element in modern warfare during the conflict in Ukraine. In the latest encounter, NATO forces used equipment worth billions of dollars to counter Russian drones that were made of wood and foam.

This article has been updated.