The police chief in Turkey's biggest city, Celalettin Cerrah, said they suspected a bomb caused the blast that 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 said.

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 agency often carries statements by Kurdish rebels.

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.

Following initial reports that 17 people were injured, the government's emergency office and Cerrah put the number hurt at 16, including seven policemen and nine civilians, two of whom were in serious condition, Cerrah said.

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

The PKK, blacklisted as a terrorist organization by Turkey, the United States and the European Union, 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 the PKK called off a five-year unilateral ceasefire in June 2004.

Thursday's blast followed reports that PKK's jailed leader Abdullah Ocalan had suffered a heart attack in prison, which Turkish officials denied.

The PKK and its sympathizers have often expressed concern over Ocalan's health and staged violent protests calling for him to be removed from solitary confinement on the prison island of Imrali in northwestern Turkey, where the 57-year-old rebel chieftain is the sole inmate.

A senior PKK commander said Thursday that anger was boiling within the group over Ocalan's conditions.

"Our anger is at a peak point, the guerrilla forces are outraged," Duran Kalkan told the Firat news agency. "Those who have put Ocalan into a process of annihilation are playing with fire."