KABUL, Afghanistan — A Toyota Corolla packed with explosives rammed a pair of American military vehicles in the Afghan capital, Kabul, on Thursday, setting off a blast that killed at least 16 people, including 6 American military advisers, and shook the relative calm that has prevailed for months in the city, Afghan officials said.

The explosion was powerful enough to rattle windows across Kabul. It left bodies strewed along the street and one of the American vehicles — an armored Chevrolet Suburban that weighed nearly five tons — lying in ruins more than 30 feet from the blast site.

Hezb-i-Islami, a relatively small insurgent faction that often competes with the Taliban for influence, claimed responsibility for the attack, which also wounded more than three dozen Afghans. Haroon Zarghon, the group’s spokesman, reached by telephone in Pakistan, said the bombing was carried out by a 24-year-old man who had grown up south of Kabul.

More attacks against Americans will come soon, Mr. Zarghon added, saying that Hezb-i-Islami was dismayed by the current talks between Afghanistan and the United States about a long-term security deal under which thousands of American soldiers could be based in Afghanistan for years to come.