Ahuge explosion rocked the diplomatic district of the capital on Saturday morning, killing seven people and wounding 91, most of them on their way to work. The brunt of the explosion was borne by civilian workers at the transportation ministry and Afghan Army guards at the entrance to the headquarters where Gen. Stanley A. McChrystal, the commander of the International Security Assistance Force and all coalition forces in Afghanistan, has his offices. A Taliban spokesman claimed responsibility for the blast. “The target was the U.S. embassy, but we could not reach it. The suicide car bomber exploded the bomb near the I.S.A.F. headquarters and killed several foreign troops,” the spokesman, Zabihullah Mujahid, told Reuters by telephone from an undisclosed location. The blast occurred in one of the city’s most heavily guarded streets, which runs between the United States Embassy and the presidential palace. The embassy is about 100 yards from the site of the explosion, but heavy barriers and blast walls protect it from the street. The palace is about 200 yards away in the opposite direction. The north end of the street is closed around the embassy, but the south end is open to allow access for Afghans working in several government buildings.