(CNN) -- President Barack Obama has expressed regret over a NATO air strike earlier in the week that resulted in the deaths of nine Afghan boys, according to a White House statement released Thursday. The president, during a video teleconference Wednesday with Afghan President Hamid Karzai, indicated his "deep regret for the tragic accident in Kunar Province," the statement said.  Obama "conveyed his condolences to the Afghan people and stressed that he and (top American commander Gen. David) Petraeus take such incidents very seriously." Obama and Karzai "agreed that such incidents undermine our shared efforts in fighting terrorism," the statement said. U.S. Lt. General David Rodriguez released a video statement earlier Thursday describing the incident.  Rodriguez said that on Tuesday, insurgents in mountains above a coalition base launched a rocket attack that wounded a U.S. civilian. Troops returned fire, and insurgents later shot another rocket at the troops. Two attack helicopters flew to the location where "they were told the rockets came from," identified who they thought were insurgents and killed nine people. Later, they found that the slain people were boys cutting wood. Rodriguez called the incident "a terrible mistake" and promised disciplinary action if warranted. Civilian casualties during warfare in Afghanistan have hurt NATO's International Security Assistance Force.  The statements from top U.S. officials reflect the high priority coalition leaders place on avoiding such accidents. Rodriguez said such incidents are "rare" when considering all of the operations the coalition undertakes.  He said a lot of time is spent training soldiers on how to "engage the right targets," and directives are constantly reviewed. "We have done much better preventing civilian casualties," he said. "But we acknowledge we have to do better." Rodriguez said the military understands families' grief over such deaths, and he said soldiers "feel worse than they can express" when they "do something terrible like mistakenly killing young boys." "They have to live with that for the rest of their lives," he said. Rodriguez also urged Afghans to help their security forces battle insurgents. His statement followed a public apology Wednesday from Petraeus. "We are deeply sorry for this tragedy and apologize to the members of the Afghan government, the people of Afghanistan, and, most importantly, the surviving family members of those killed by our actions," Petraeus said. "Regrettably, there appears to have been an error in the hand-off between identifying the location of the insurgents and the attack helicopters that carried out the subsequent operations." Karzai condemned the incident "in the strongest terms possible." He noted the incident occurred less than 10 days after another incident "that left many civilians dead in the same province." On February 20, Kunar Gov. Sayed Fazlullah Wahidi said 64 civilians had died in a joint operation by ISAF and Afghan security forces over several days. The dead included 20 women and 15 children, he said. Petraeus recently directed military commanders in Afghanistan to review changes meant to minimize civilian casualties. He has ordered commanders to brief helicopter attack crews again on the changes, he said.
NEW: Obama expresses regret for the deaths of the Afghan boys . Helicopters mistakenly killed nine boys chopping wood . Civilian casualties have hurt the coalition's efforts over the years . More than 60 civilians were killed during a February operation .