NATO has vowed to investigate an airstrike in southern Afghanistan that local officials say killed a child.

The coalition force said on Friday it would investigate reports of the child's death.

Afghan President Hamid Karzai said the strike on Thursday in Helmand demonstrated the U.S. does not respect the lives of Afghan civilians.

Civilian casualties have been one of the most sensitive issues of the 12-year military intervention in Afghanistan.

Karzai warned that the latest incident threatened the proposed bilateral security agreement with Washington. The deal is aimed at shaping a U.S. military presence in Afghanistan after 2014, when most foreign forces are due to leave the country.

Washington is pressing the Afghan government to sign the new security pact or face the prospect of no U.S. troops in the country beyond 2014.