WARSAW, Poland (AP) — European leaders on Thursday expressed alarm over growing Russian hostility threatening their countries as Moscow’s forces pursue their invasion of Ukraine — concerns exacerbated by events of the previous day when multiple Russian drones struck Polish soil.

The incursion into Poland, which came during unrelenting Russian strikes on neighboring Ukraine, deepened longstanding fears that the three-year war between Poland’s neighbors could precipitate a wider conflict. U.S.-led efforts to steer Moscow and Kyiv toward a peace settlement have so far failed to get traction.

European officials described the incursion as a deliberate provocation, forcing the NATO alliance to confront a potential threat in its airspace for the first time and compelling it to take stock of its military response and capabilities.

British Prime Minister Keir Starmer spoke about the incursion with French President Emmanuel Macron and German Chancellor Friedrich Merz on Thursday.

Starmer’s office said that it “was clear that Russia was continuing to ramp up its aggression, systematically stepping up its attacks through a campaign of increasingly belligerent actions.” The German government said it will “extend and expand air policing over Poland.”

NATO’s supreme commander in Europe, U.S. Gen. Alexus Grynkewich, said Thursday that the alliance wasn’t certain about the number of drones that entered Polish territory, nor whether they were fired intentionally.

“But we will learn lessons. We will learn of things that we need to enhance our posture, to handle these limited incursions,” Grynkewich said in Vilnius, Lithuania.