A suicide bomber hit a minibus carrying foreign security guards and caused several casualties on Monday in Kabul along the main road to the eastern city of Jalalabad, police said.
The attacker was on foot, according to police, who refused to give a toll but said there were "multiple casualties" among the bus passengers who were "employees of a foreign compound".
The bus was carrying Nepalese guards, according to an AFP cameraman, who also reported more than two dozen ambulances at the scene.
It is the first attack in Kabul since the start of holy fasting month of Ramadan on June 6. The last attack in the Afghan capital on April 19 left 64 dead and more than 340 wounded.
That attack was claimed by the Taliban, who have been waging an insurgency against the Western-backed Kabul government since they were ousted from power by a US-led invasion in late 2001.
Washington recently announced an expansion of the US military's authority to conduct air strikes against the Taliban, significantly boosting Afghan forces who have limited close air-support capacities.
US forces have been in an advisory role in Afghanistan since the start of 2015 and were only authorised to hit Taliban targets for defensive reasons, or to protect Afghan troops.
The changes mean US troops can now work more closely with local fighters in striking the Taliban, who have demanded the departure of all foreign forces.