Washington(CNN) Iran appears to be modifying the attack drones it's providing to Russia so that the explosive warheads can inflict maximum damage on infrastructure targets inside Ukraine, according to a new investigative report obtained exclusively by CNN. "Last month, the Institute for the Study of War found that Russian forces had become increasingly reliant on the drones in their campaign against Ukrainian critical infrastructure -- so much so that their stockpile of the drones is already running low, just months after Iran began sending them. All Rights Reserved