"It is their decision to make. We have not encouraged them to do that. We have been very clear about our concerns over escalation here," Kirby told reporters.
Previously, reports suggested that Kiev was behind the recent drone attacks on airfields in the Russian regions of Kursk, Ryazan and Saratov, citing a high-ranking Ukrainian official.
Since the beginning of the Russian special operation in Ukraine, Washington adopted several sanction packages against Moscow and allocated billions in military aid for Kiev.