Poland’s president said on Wednesday that a Ukrainian air defense missile had most likely caused a deadly explosion in his country a day earlier, calling it an “unfortunate accident” and easing fears that his country and its NATO allies could be drawn into a direct conflict with Russia.

President Andrzej Duda said early indications suggested that Ukrainian efforts to counter a barrage of roughly 100 Russian missiles had been the cause of the blast on Tuesday — not a direct attack on his country.