A loud explosion rocked the center of the Afghan capital on Sunday after an apparent suicide attack against a convoy of foreign troops, a security official said.
The official, speaking on condition of anonymity, said initial reports suggested a suicide attack.
"It was during rush hour and there are casualties," he added.
The attack in Kabul came during a period of heightened tension following intense fighting between government troops and the Taliban around the northern city of Kunduz, which fell briefly to the insurgent Islamist movement at the end of last month.