President Hamid Karzai has accused the US of killing seven children and a woman in an airstrike in central Afghanistan - an incident set to further damage frayed ties between the two allies, Te Sky News reported. "As a result of bombardment by American forces last night, which was conducted... in Siahgird district of Parwan province, one woman and seven children were martyred and one civilian injured," a statement from his office said on Wednesday. Civilian casualties have been one of the most sensitive issues of the 13-year military intervention in Afghanistan, and Karzai has often used accidental shootings and misguided airstrikes to berate foreign countries and stir public anger. Relations between Washington and Kabul have been rocky for years, and negotiations over an agreement that would allow some US troops to remain in the country after this year have broken down into a long-running public dispute. Karzai made a surprise decision not to sign the bilateral security agreement (BSA) late last year despite having vowed to do so, leading to the threat of a complete withdrawal of US-led NATO troops by the end of 2014.