Kabul, Afghanistan (CNN) -- The U.S. military slammed a drone crew Saturday for "inaccurate and unprofessional" actions behind a drone strike that killed nearly two dozen civilians in Afghanistan this year.
The military has been investigating a February 21 drone strike in southern Afghanistan's Uruzgan province. The attack killed 23 civilians and wounded 12 others. It was carried out by a Predator drone, an unmanned aircraft that is frequently used to attack insurgents and militants in Afghanistan and Pakistan.
The military also disciplined six officers and called for improvements in counter-intelligence training to avoid civilian deaths in combat, which have undermined the credibility of NATO-led forces in Afghanistan and the Afghan government.
"Our most important mission here is to protect the Afghan people; inadvertently killing or injuring civilians is heartbreaking and undermines their trust and confidence in our mission. We will do all we can to regain that trust," said Gen. Stanley McChrystal, the top U.S. military commander in Afghanistan.
In the Uruzgan incident, coalition aircraft attacked three vehicles with more than 30 civilians who were mistaken for insurgents, according to U.S. Army Maj. Gen. Timothy McHale, who reviewed the incident.
The Predator crew "ignored or downplayed" intelligence that the "convoy was anything other than an attacking force," the report said. The tragedy "was compounded by a failure of the commands involved to timely report the incident," it said.
"The strike occurred because the ground force commander lacked a clear understanding of who was in the vehicles, the location, direction of travel and the likely course of action of the vehicles," he said.
"This lack of understanding resulted from poorly functioning command posts....which failed to provide the ground force commander with the evidence and analysis that the vehicles were not a hostile threat and the inaccurate and unprofessional reporting of the Predator crew operating out of Creech (Air Force Base in) Nevada which deprived the ground force commander of vital information," McHale said in his report.
After reviewing McHale's investigation, McChrystal issued reprimands to four officers, including senior leaders at the battalion and brigade level, and admonishments to two junior officers.
The review cited "several shortcomings in training, communication and decision-making" and the military will implement improvements.
One will be a "rigorous series of challenging counterinsurgency training scenarios" and the "use of case studies and vignettes to better educate and train for leading" counter-insurgency operations.
Another will be the development of a mobile training tream "to evaluate and train unit command posts" on counter-insurgency operations and developing a "program to better educate and train for leading" such operations.
"This will include intensive training on the process of identifying and engaging combatants in according with rules of engagement and tactical directives that govern operational conduct."