Poland is investigating a possible violation of its airspace overnight, the Operational Command of the Armed Forces said.

The military and police are working to locate a possible crash site south of the city of Lublin, in eastern Poland, where an unidentified object might have fallen, the Command said in a statement Sunday.

While no violation has been confirmed, the teams are trying to verify a recorded radar signal and reports from residents nearby and to determine whether the signal may have been triggered by some kind of weather phenomena, it said.

“It could have been a meteorological event that disrupted the operation of our radar systems, or a large flock of birds,” Command spokesman Jacek Goryszewski said on public television. “We also cannot rule out the possibility that it was a larger drone that was detected by our stations.”

NATO member Poland, which borders war-torn Ukraine, has stepped up its air defenses and boosted its rapid-response systems as it contends with rising provocation from Russia. Polish jets have intercepted Russian reconnaissance planes near its Baltic Sea coast in recent weeks, and Prime Minister Donald Tusk last month tied a fire at a facility operated by the country’s largest drone maker to Russia, calling it “an act of sabotage.”In July, an investigation determined that an object that entered Poland’s airspace during a major Russian attack on Ukraine was a Russian missile.

Tusk has warned that Russia plans to launch “hybrid-style” drone and missile strikes against nations supporting Ukraine, including Poland, as the war enters its most crucial phase.