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.

It was the latest in a series of airspace incursions in countries on NATO’s eastern flank, including Romania and the Baltic states, that have fueled fears of the war in Ukraine spilling over the alliance’s borders.

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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 percent certain about the type of missile and who launched it,” Tusk told an emergency meeting.