KYIV, Ukraine (AP) — The Kremlin claims Ukrainian drones have struck two air bases deep inside Russia. Hours later, Russia unleashed another massive missile barrage across Ukraine, striking homes and buildings and killing civilians. The targeting of the Russian air bases threatened a major escalation of the nine-month war because it hit an airfield that houses bombers capable of carrying nuclear weapons. Russian President Vladimir Putin has threatened to use all available means to defend Russian territory, a remark many have interpreted to include nuclear weapons. It was the first time since the conflict’s start that such a base has been attacked.