(ANSA) - BELGRADE, SEP 10 - The drone incident in Poland is "extremely serious," according to Italian President Sergio Mattarella, who spoke from Ljubljana on the first leg of his visit to Slovenia. What is going on in Ukraine is also exacerbated by "the Kremlin's threatening statements to European countries, which are a source of concern. "The risk of escalating into an uncontrollable conflict is extremely high," Mattarella stated. Slovenian President Nataša Pirc Musar stated, "I can't accept Russia's explanation that it was a mistake; I don't believe it was. "Let us wait to hear NATO's response," she noted, speaking from Ljubljana after meeting with President Sergio Mattarella. (ANSA).