Four former U.S. Air Force drone operators issued a public letter on Wednesday warning that the United States' ongoing targeted killing program "is one of the most devastating driving forces for terrorism and destabilization around the world."

The letter (pdf), addressed to U.S. President Barack Obama, Defense Secretary Ashton Carter, and CIA Chief John Brennan accuses the administration of fueling "tragedies such as the attacks in Paris" while "lying publicly about the effectiveness of the drone program."

"We came to the realization that the innocent civilians we were killing only fueled the feelings of hatred that ignited terrorism and groups like ISIS," the whistleblowers wrote, "while also serving as a fundamental recruitment tool similar to Guantanamo Bay."

According to Guardian reporters Ed Pilkington and Ewan MacAskill, who broke the story, the servicemen have "more than 20 years of experience between them operating military drones." In the letter, the men say they all "succumbed to PTSD" and were subsequently "cut loose by the same government we gave so much to—sent out in the world without adequate medical care, reliable public health services, or necessary benefits."

Facing possible persecution for speaking out, the men are being represented by attorney Jesselyn Radack, director of national security and human rights at the nonprofit ExposeFacts. Radack says this letter marks the "first time we’ve had so many people speaking out together about the drone program."

The full text of the letter is below: