Human error was the cause of the Sept. 17 airstrike that killed more than 60 Syrian troops near Dayr Az Zawr, U.S. Central Command officials said Tuesday.
After nearly three months of review, investigators determined U.S. and coalition forces mistakenly concluded the targets were affiliated with the Islamic State of Iraq and Syria, or ISIS, according to a statement from the command.
While the strike was based on a "reasonable interpretation" of available information and conducted without "deliberate disregard," an American general acknowledged it was a mistake and likely hit forces aligned with the government of Syria.
"In this instance, we did not rise to the high standard we hold ourselves to, and we must do better than this each and every time," Lt. Gen. Jeff Harrigian, head of U.S. Air Forces Central Command, said in the statement.
Harrigian has ordered changes to improve the targeting process, including better information sharing among analysts and more frequent use of a U.S.-Russia hotline designed to prevent accidents and miscommunication in the war zone.
During a phone call with reporters, Air Force Brig. Gen. Richard Coe, the investigating officer, said the day of the strike the Russians actually used the phone line to help stop the attack.
"It's because we called the Russians with the information that we'd be striking [Dayr Az Zawr] area that the Russians had the chance to call back to the [Combined Air Operations Center] on that phone line and pass us critical information that could halt the strike," he said.
It wasn't immediately clear why, if U.S. forces communicated with their Russian counterparts before the mission, they weren't warned against carrying it out.
Coe noted the Russians aren't responsible for helping the U.S. and its allies validate targets on the ground. "That's the coalition's job," he said. At the same time, Coe acknowledged the strikes would have continued were it not for the second call from the Russians.
U.S., Australian, U.K and Danish aircraft participated in the bombing run, including F-16 fighter jets, A-10 ground-attack jets, F/A-18 fighter-attack jets and drones, Coe said. The warplanes released 34 precision-guided bombs, and 380 rounds of 30 mm ammunition, he said. Targets included vehicles, fortified locations, tunnels, tents and personnel, he said.
At the time, the Russian defense ministry stated coalition aircraft killed more than 60 Syrian troops and wounded roughly 100 more. Investigators couldn't determine "with certainty" the number or identity of those killed or wounded, but it's highly likely that those struck "were aligned with the Syrian government," Coe said.
"We could only substantiate 15 deaths, but we know the Syrian Observatory for Human Rights reported … 83 were killed on the day of the attack," Coe said. "We certainly believe more than 15 were killed in the attack."
Investigators received testimony from more than 70 U.S. and coalition personnel and reviewed intelligence reports and surveillance images to determine what went wrong, Coe said.
Teams at the time were following a vehicle "for many hours" through overhead surveillance, Coe said. As surveillance planes gathered intelligence from the skies, markings on equipment on the ground "were still indistinguishable," he said. In addition, the forces on the ground were not wearing recognizable military uniforms, and coalition officials didn't observe identifying flags or unit markings.
"In many ways, these forces looked and acted like the Da'esh forces the Coalition has been targeting for the last two years," he said.
Even so, at least one intel analyst remarked at the beginning of the operation, "what we're looking at could not possibly be ISIL," Coe said, using another name for ISIS. "But at the time, that data analysis was not pushed to a larger group, nor to the final decision-makers," he said, "because people were already certain that the target was fully validated."
Also playing a role in the incident was the use of multiple targeting methods -- deliberate and dynamic -- in a single mission, Coe said. Deliberate or pre-validated targets are assessed over days or weeks, while dynamic or coveted targets of opportunity are considered in real-time. "Blending these two processes seems to have allowed the planners to not fully and critically second-guess their conclusions as the situation developed," Coe said.
Another contributing factor was simple miscommunication.
The first strike location described to the Russians was off "by several kilometers," Coe said. The CAOC official in the first phone conversation with a Russian counterpart mistakenly said airstrikes would begin "nine kilometers south of the Dayr Az Zawr airfield when in fact they were planned nine kilometers south of the city," which is north of the airfield, he said.
What's more, the Russian official who called back to notify the CAOC of the misguided strikes waited to speak to his usual point of contact instead of the colonel who answered, Coe said. By the time his counterpart had come to the phone, 27 minutes had passed before a ceasefire was called, he said.
Ultimately, confirmation bias, invalid assumptions, and misidentification of forces on the ground led to the errant strike, Coe said.
Russian officials didn't participate in the investigation, the general said.
Russia's initial response through the Kremlin-funded news outlet RT was to cite previous condemnations of the airstrikes by Syrian President Bashar al-Assad.
"It was not an accident by one airplane, it was four airplanes which kept attacking the position of the Syrian troops for nearly one hour or maybe a little bit more," Assad said in September. The head of the regime charged that the U.S. coordinated the airstrikes with ISIS. He noted that the militants attacked Syrian troops immediately after the airstrikes.
RT also cited Syrian Foreign Minister Walid Muallem as charging that "it was a deliberate attack, not a mistake -- even if America says the opposite."
The attacks came as Secretary of State John Kerry was trying to extend a fragile "cessation of hostilities" in Syria's civil war.
Before the Dayr az Zawr airstrikes, the U.S. had charged that Russian and Syrian bombing of hospitals and a United Nations aid convoy were endangering the cessation of hostilities. The cessation fell apart shortly after the coalition airstrike on the "Syrian aligned" forces.
A spokesman for the British Defense Ministry backed up the U.S. version of the airstrikes, saying they were "made in good faith," the BBC reported.
"We welcome the coalition's report and its conclusion that the decision to identify the targets as Daesh (ISIS) fighters was reasonable," the ministry said in a statement. "We would not and did not intentionally strike known Syrian Regime military units."
-- Richard Sisk contributed to this report.