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A police bus was badly damaged in the blast, which Istanbul police chief Huseyin Capkin said had been set off by remote control, in the Sutluce district, as the vehicle drove past.
"It appears that it [the bomb] went off as a police vehicle with 21 officers inside passed by," he said, adding that the explosives may have been placed on a motorcycle.
The police officers had been on duty at a nearby conservative business association building, the BBC reported.
Capkin said his teams were carrying out an investigation, but that none of the police officers were seriously injured.
Al Jazeera reported that forensic teams covered the bus in blue nylon sheets, while police sealed off the area and searched for fragments of the bomb.
No group immediately claimed responsibility for the attack, but the BBC reported that it has been linked to an attack on a bus stop last year blamed on Kurdish rebels.