A suicide attacker blew himself up next to a bus carrying army personnel in the Afghan capital on Wednesday, wounding at least six people, officials said.
The situation remains unclear but no deaths have been reported, defence ministry deputy spokesman Dawlat Waziri said. Western security sources confirmed the attack.
An AFP photographer said that ambulances were carrying the wounded to hospital after the attack on the bus, which took place on a main street in Kabul.
Spokesmen for the defence and interior ministries said that six people had been wounded. According to a police official on the scene most of the passengers on the bus were hurt and the bomber struck on foot.
Interior ministry spokesman Sediq Sediqqi said the suicide bomber detonated "a little bit away from the back of the bus," which could explain the low casualty numbers released by the Afghan authorities.
There was no immediate claim of responsibility, but the Taliban and other insurgents waging an 11-year fight against the Western-backed government have carried out a series of bomb attacks in the heavily protected capital.
On January 21, a squad of Taliban suicide bombers stormed the Kabul traffic police headquarters, killing three police officers and unleashing a stand-off that lasted for more than eight hours.
On Sunday, officials said police shot dead a would-be suicide bomber in Kabul's diplomatic enclave.