15 Killed, Including 6 Americans, in Kabul Suicide Car Bombing

A suicide car bomber attacked a NATO convoy in the Afghan capital on Thursday, killing two U.S. troops and four American civilian contractors.

Eight Afghans civilians, including two children also died in the explosion and more than 30 were wounded.

The Islamist group Hezb-e-Islami claimed responsibility, saying it marked the beginning of a new military campaign against Americans.

The group said its fighters had stalked the Americans for a week to learn their routine before striking.

It was the deadliest attack to rock the Afghan capital in more than two months and followed a series of other attacks against Americans that has made May the deadliest month for international forces this year with 18 fatalities.

U.S.-led forces are increasingly leaving the fighting to their Afghan counterparts and focusing more on training missions. The international combat mission is scheduled to finish by the end of 2014.

Cmdr. Bill Speaks, a spokesman for the U.S. Defense Secretary, confirmed that two American soldiers were killed. Security company DynCorp International said four of its American civilian contractors were among the dead.

President Hamid Karzai, pictured, condemned the attack, saying it was the work of "terrorists and enemies of Afghanistan's peace."

Hizb-e-Islami, which is a rival of the Taliban movement as well as the Americans, is headed by 65-year-old Gubuddin Hekmatyar, a former Afghan prime minister and one-time U.S. ally, who is now regarded as a terrorist by the U.S. The militia has thousands of fighters and followers in the country's north and east.

NATO’s International Security Assistance Force commander Gen. Joseph Dunford said: "While today’s attack shows the insurgents remain dangerous, they are not a threat to the Afghan Government and its forces. In the end, today’s tragedy shows that the insurgents can offer no positive vision for the future."

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