Six Americans — two soldiers and four civilian contractors — are among at least 14 people killed in a massive car bomb blast in Kabul this morning, according to U.S. and Afghan officials.

More than 30 Afghan civilians, including a number of children, were wounded.

The attack happened just after 8 a.m. The bomber drove a car filled with explosives directly into a military convoy as it drove through the city. The explosion was so powerful it reduced a series of vehicles to piles of twisted, mangled metal, and set nearby buildings on fire. The scene was quickly secured by NATO troops, as fires smoldered on the freshly blackened street. Some of the bodies were so badly burned they were difficult to identify.

The militant group Hezb-Islami, run by notorious Afghan warlord Gulbuddin Hekmatyar, quickly claimed responsibility, saying they targeted a convoy carrying American military advisers. A statement by the group’s spokesperson says it has formed a special cell to carry out attacks on U.S. targets