KABUL - A NATO airstrike that Afghan officials said Wednesday killed nine children collecting firewood in eastern Afghanistan the day before became the latest irritant in the tense relationship between President Hamid Karzai and the international force in the country.

Gen. David H. Petraeu, the top NATO commander here, issued an apology for an error that military officials attributed to faulty communication as an air weapons team responded to an attack on a NATO base Tuesday in Konar province.

"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 in an unusually contrite written statement. "These deaths should have never happened and I will personally apologize to President Karzai."

The strike increased the already high tension between Karzai and NATO commanders, who came under scrutiny late last month because of another case in which Afghan officials alleged that dozens of civilians were killed in a U.S. military operation, also in Konar province.

NATO officials have said they are investigating the earlier case but have resisted the account of Afghan officials, who said 65 civilians were killed.

"Poor and innocent civilians . . . have continued on [a] daily basis to suffer in the unjustifiable operations and bombings carried out by the NATO," Karzai's office said in a statement released before Petraeus's apology.

The statement said that as long as civilians are killed by NATO strikes, "fighting terrorism in Afghan villages can have no success."

NATO officials said coalition forces launched the strike in response to a rocket attack on Forward Operating Base Blessing, in Konar's Darah-Ye Pech district. Troops used artillery and opened fire from aircraft, targeting the area from where the attack on the base had originated, officials 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 subsequent operations," the NATO statement said.

Petraeus said the error was "particularly distressing given the recent direction I gave to commanders to review our tactical directive that is intended to reduce civilian casualties to the absolute minimum."

NATO said it will investigate the incident and will take disciplinary action against those responsible, if necessary. Petraeus said he had ordered all helicopter attack crews and NATO commanders "to be re-briefed on the tactical directive, reinforcing the need to be sure we protect the lives of innocent Afghans as we pursue a ruthless enemy."

Fazlullah Wahidi, the governor of Konar, said the rockets were fired around 11 a.m. About an hour later, NATO helicopters were hovering around Monogai district, where the rockets' suspected launch site is located.