A bomb placed on a bicycle and detonated by remote control exploded next to a police bus in Kabul on Tuesday, wounding 11 people, police said.
The explosion wounded both police and civilians, said Abdul Rahman Sarjang, a police officer at the scene.
"I just heard an explosion and saw a big plume of smoke," said Barat Noori, who works in a nearby bakery. He helped the injured policemen and civilians into taxis that took them to the hospital.
Police at the scene picked through the twisted remains of the bicycle bomb. The windows on the bus were shattered but it was not otherwise heavily damaged, and police drove it away about an hour after the 8 am attack.
"They are targeting police," said Jan Agha, a police officer at the scene. Agha complained that his $50 monthly salary was not worth the increasing risks that police are facing.
Militants have been stepping up attacks, including roadside and suicide bombings, across Afghanistan the last several months.
Foreign troops and Afghan security forces are the most frequent targets.
A suicide bomber killed 12 people and injured 40 late last month outside the gates of the Interior Ministry, which oversees the country's police force.