Kabul, Afghanistan (CNN) -- Eight Afghan youths killed in a coalition airstrike last week were mistaken for potential attackers, the International Security Assistance Force said Wednesday.
Ground forces observing the village in Kapisa province, northeast of Kabul, "identified several groups of adult-sized Afghan males that were leaving the village at different times and in different directions," U.S. Brig. Gen. Lewis Boone, ISAF spokesman, told reporters.
"One of these groups, consisting of eight persons, appeared to be carrying weapons and heading for the nearby mountains," he said. "They were observed moving in open terrain in a tactical fashion, clearly keeping distance from each other. After approximately 500 meters they were seen to gather under a large boulder."
"Their purposeful movements and the weapons they were seen to be carrying led the ground commander to believe this group was getting ready to attack and were an imminent threat to the Afghan National Police and coalition forces in the valley," Boone said.
As ground forces and air support continued to observe, the aircraft dropped two bombs on the group, he said.
"Despite all tactical directives being followed precisely, we now know the unfortunate results of this engagement," Boone said. "In the end, eight young Afghans lost their lives in this very sad event. We again pass our most sincere condolences to the families and loved ones of those who died."
NATO also expressed "deep regret" in the wake of the airstrike.
"While the exact circumstances of this tragic incident remain to be determined, ISAF is taking appropriate action to ascertain the facts, and prevent similar occurrences in the future," NATO said in a statement.
Afghan President Hamid Karzai strongly condemned the strike last week.
Gen. John R. Allen, ISAF commander, has met with the provincial governor to express condolences, Boone said Wednesday. "As commander, he takes these terrible events very seriously and is committed to eliminating them completely."
Civilian deaths as a result of action by the NATO-led international coalition have long caused anger in Afghanistan, adding pressure on international forces to withdraw.
The international force has said avoiding civilian casualties is a high priority, a pledge it repeated following the recent deaths.
"My command's mission is to protect the civilian people of Afghanistan," Allen said earlier. "I take very seriously the loss of every Afghan life. We will continue to do all we can to ensure the safety of the Afghan population."
Boone said Wednesday, "Though we can never bring these young Afghans back to their families, we in the very least are promising to help this small community by other means in hopes that we may in some way improve their daily lives."
The number of ISAF-caused civilian deaths decreased by nearly 17% from 2010 to 2011, the coalition force said in its December monthly report.
Insurgents caused more than 85% of civilian deaths and injuries in 2011, according to the report.
CNN's Barbara Starr and Jennifer Deaton contributed to this report.