KABUL, Afghanistan - A suicide car bombing tore through a U.S. convoy in Kabul on Thursday, killing at least 15 people including six Americans in a blast so powerful it rattled the other side of the Afghan capital.
U.S. soldiers rushed to help, some wearing only T-shirts or shorts under their body armor.
A Muslim militant group claimed responsibility for the morning rush-hour attack, saying it was carried out by a new suicide unit formed in response to reports that the U.S. plans to keep bases and troops in Afghanistan even after the 2014 deadline for the end of the foreign combat mission.
The group, Hizb-e-Islami, said its fighters had stalked the Americans for a week to learn their routine before striking - a claim that raises questions about U.S. security procedures.
Two American soldiers were killed, as were four American civilian contractors with DynCorp International. DynCorp, based in Falls Church, Va., said its employees were working with U.S. forces training the Afghan military when the blast occurred.
It was the deadliest attack to rock Kabul in more than two months and followed a series of other assaults on Americans, even as U.S.-led forces are focusing more on training while leaving the fighting to Afghans.
Thursday's bombing pushed the monthly toll for the U.S.-led coalition to 18, making May the deadliest month so far this year. By comparison, 44 international troops were killed in the same period last year. The overall number of coalition deaths has dropped as Afghan forces increasingly take the lead.
The suicide bomber detonated his car about 8 a.m. and set nearby buildings on fire. The blast left body parts scattered on the street along with the wreckage of one of the U.S. vehicles.
Kabul Deputy Police Chief Daud Amin said it was difficult to count the dead.
"We saw two dead bodies of children," Amin said. "But the rest of the bodies were scattered around." Thirty-five Afghans were wounded, according to the Health Ministry.
Kabul had been enjoying a relative lull in attacks in recent weeks. The last major assault was March 9, when suicide bombers struck near the Defense Ministry while U.S. Secretary of Defense Chuck Hagel was visiting.
President Hamid Karzai condemned Thursday's attack, saying it was the work of "terrorists and enemies of Afghanistan's peace."
A spokesman for the Hizb-e-Islami militant group, Haroon Zarghoon, told The Associated Press that one of its operatives carried out the attack on two vehicles of U.S. advisers.
"The cell had been monitoring the movement and timing of the American convoy for a week," Zarghoon said.
U.S. Toll in Afghanistan
Source: Department of Defense