The city's police chief Celalettin Cerrah said they suspected a bomb caused the blast which rocked the Bayrampasa district on the European side of the city straddling the Bosphorus Strait.

"It looks like it (the blast) was caused by explosives," Cerrah told reporters at the scene, the Anatolia news agency reported.

The Europe-based, pro-Kurdish Firat news agency reported on its website that an anonymous person claimed responsibility for the blast on behalf of the Kurdistan Freedom Falcons (TAK) in a telephone call to the agency.

No other details were available.

The explosion ripped through the cafe located behind the local headquarters of the riot police and frequented by officers at 2:05 p.m. (1205 GMT), blowing out the windows of nearby buildings.

Istanbul chief prosecutor Aykut Cengiz Engin told reporters at the scene that seven police officers and 10 civilians, including passers-by, were injured in the explosion.

"The officers are in good condition. One of the civilians is in a serious condition," he said, according to Anatolia.

Cerrah had earlier announced that a child had suffered serious injuries in the blast.

Turkish officials say TAK is a cover group used by the outlawed Kurdistan Workers' Party (PKK) to carry out attacks on civilian targets that would draw international condemnation.

The PKK, however, denies any link to TAK.

TAK has been blamed for a series of bomb attacks in Turkey last year, including one in the Aegean resort of Kusadasi in July that killed five people, including two foreign tourists.

The PKK, blacklisted by Turkey, the United States and the European Union as a terrorist organization, has been fighting the Ankara government since 1984 when it picked up arms for self-rule in the country's mainly Kurdish southeast.

The conflict has claimed some 37,000 lives.

Unrest in the southeast of Turkey has increased markedly since last year after PKK rebels called off a five-year unilateral ceasefire in June 2004.