A bomb placed on an electric bicycle exploded in Istanbul on Wednesday, wounding seven people, Istanbul's police chief said.
Huseyin Capkin told reporters none of the wounded were in a critical condition and noted the explosion occurred near a police school in Etlier, a residential and shopping district. Police have frequently been targeted by militants in Turkey.
Turkey is due to vote in a parliamentary election on June 12. Security forces are on edge as there has been a rise militant activity in recent weeks related to a long-running Kurdish separatist insurgency.
Prime Minister Tayyip Erdogan's AK Party is expected to score a comfortable victory in the vote to win a third consecutive term. He first come to power in 2002.
Erdogan has said he will re-write Turkey's constitution if he is re-elected, to replace one drafted in 1982 under military tutelage following a coup two years earlier.
"The aim of the attack is to prevent Turkey from discussing democracy, elections, a new constitution," said Suat Kilic, a parliamentarian from the ruling AK Party. "Terrorist organisations carry out these attacks before every election."
"The attack aims to prevent AKP from gaining enough seats to change the constitution," Kilic said.
CNN Turk quoted Istanbul provincial health manager saying that of the seven wounded, two had serious injuries.
Television images showed one young woman being stretchered to an ambulance with an oxygen mask covering her face.
"We thought the building had collapsed. I even thought that a plane crashed into the next garden. Everybody was in panic," Ilhan Kurt, a pharmacist, said.
Watching from his shop across the road he saw a handful of people getting off a bus that had been passing by when the explosion occurred.
"Some people were holding their ears, who I think were injured. Three or four people got out of a bus."
The site of the blast was cordoned off as white-suited forensic teams combed the area, with droves of police cars and ambulances parked nearby.
According to a resident living nearby, the explosion happened around the tail-end of the morning rush hour, at around 9 am.
"It wasn't like gunfire. It was like an explosion," Tuncay Ozdemircan said.
"When I looked out of the window I saw yellow and white smoke rising, and I thought that it was a bomb," he said.