Estonia is extending a fence along its border with Russia and building anti-tank ditches and bunkers in preparation for a potential conflict with Moscow. But those defenses won’t guard against the threat it and its NATO allies face from Russian drones and electronic warfare.

In the week since NATO fighter jets scrambled to shoot down multiple dozens of Russian drones that had crossed into alliance airspace in Poland, US and Western intelligence officials have been unable to determine whether the incursion was accidental or an intentional effort by Russia to probe western air defenses and gauge NATO’s response.

British fighter jets have embarked on their first Nato policing mission over Poland to counter “reckless Russian aggression”.

"If it had all happened at once, maybe you could call it an accident. But six hours of drones? That’s a test – a way to see what the West would do. And we have to respond like it’s a test," Kellogg said.

Poland is tapping into Ukraine's expertise in drone warfare by setting up joint military training and manufacturing projects.

Responding to President Trump, Poland's leader said, "we would also wish that the drone attack on Poland was a mistake. But it wasn't."

President Trump offered his first reaction to Russia's drone incursion on Poland, which the country's military and European leaders condemned as "unprecedented."

It wasn’t immediately clear who was behind the flyover. But Denmark’s prime minister and NATO’s secretary-general said Tuesday that Russian involvement couldn’t be ruled out.