(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 cannot 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.