The driver found a suspicious package in the back of the vehicle after he dropped his passengers off at the Beyoglu courthouse -- the hub of the city's central European quarter -- and returned to the car park, the report said.

Bomb experts defused the device, made up of nearly a kilo (about 2.2 pounds) of plastic explosives attached to a mobile phone and primed to be set off by remote control, the agency quoted anonymous police officials as saying.

The bomb failed to explode because the phone's battery was dead, it added.

Police were investigating whether the bomb was the work of the outlawed Kurdistan Workers' Party (PKK), which has waged a bloody separatist campaign in the country's eastern and southeastern regions since 1984, Anatolia said.

The PKK, blacklisted as a terrorist group by Turkey, the European Union and the United States, has in the past conducted bomb attacks across the country, including Istanbul, a city of more than 12 million.

The latest bomb attack in the city, which injured three people last week, was claimed by a radical Kurdish group - which police says is linked to the PKK -- in reprisal for a recent wave of bloody Kurdish riots that claimed 15 lives.