( CNN ) -- A suicide car bombing targeting a coalition convoy in the heart of Afghanistan 's capital on Thursday killed at least 12 people , six Americans and six Afghans , authorities said . NATO 's International Security Assistance Force said two U.S. service members working with ISAF and four ISAF-contracted civilians died in the Kabul bombing . The four were Americans working with DynCorp International , a contracting firm based in Falls Church , Virginia , the company said . The people worked on a program that provided mentors and trainers to support the development of Afghanistan 's Defense Ministry . Three of those people were wounded . An Afghan Interior Ministry spokesman said at least six Afghan civilians were killed and 30 were injured , an Interior Ministry spokesman said . The fatalities included at least two children . ISAF commander Gen. Joseph Dunford said `` insurgents deliberately exploded a bomb today in a residential area of the most populated city in Afghanistan , '' killing and wounding dozens of Afghans . `` The insurgents use these desperate and indiscriminate acts of violence to slow the momentum of Afghanistan 's progress . The insurgents can not offer the Afghan people a better future . All they can offer is violence and oppression . '' The insurgent group Hezb-e Islami , led by Gulbuddin Hekmatyar , claimed responsibility for the attack . A one-time prime minister , Hekmatyar has been against the government and the presence of the foreign forces in Afghanistan since the fall of the Taliban regime in 2001 . He is not under the Taliban leadership , but operates alongside them . The incident comes during the Taliban 's spring offensive . `` We had planned this for days before we got a chance to target American advisers , '' said Haroon Zarghon , a spokesman for the group .
NEW : 6 Americans died in the attack and 6 Afghans . Insurgent group claims responsibility . Comment: