An object that came down in eastern Poland overnight appears to be a Russian missile, Polish Prime Minister Donald Tusk said on Thursday, after authorities found a crater and scattered debris in a field following reports of an explosion.

Poland scrambled fighter jets to secure its airspace after Russian airstrikes killed at least eight people in neighboring Ukraine in attacks that extended as far as the western city of Lviv.

"All the indications are that it was a Russian Kh-101 ballistic missile, but we want to be 100% certain about the type of missile and who launched it," Tusk told an emergency meeting.

"There was no direct threat because the missile landed in an uninhabited area. We were ready to shoot it down had it continued its flight," he added.

Ukraine's Foreign Minister Andrii Sybiha had said earlier in a post on X that a Russian Kh-101 cruise missile crossed into Poland.