The NATO-led force in Afghanistan said it would investigate Thursday's airstrike in Helmand that local officials say killed a child and has further aggravated a stand-off between the Afghan president and the U.S. government.
"ISAF deeply regrets any civilian casualties caused by this airstrike," the force said in a statement.
President Hamid Karzai said the killing demonstrated the United States did not respect the lives of Afghan civilians and if such attacks continued, he would not sign a bilateral security pact.
Wrangling over the deal has lasted about a year. The pact aims to shape a U.S. military presence in Afghanistan after 2014, when most foreign forces are due to leave the country. Without a pact, U.S. officials have warned the United States could pull out all of its troops.