Police are still looking for the individual who detonated the remote-control bomb, Istanbul Governor Huseyin Avni Mutlu told reporters.

Radical Kurdish militants claimed responsibility for the roadside bomb that blew up a bus carrying army personnel in the suburb of Halkali Tuesday, killing four soldiers and the teenage daughter of an officer and leaving 14 people wounded.

Some of the suspects had already been arrested Monday as part of a probe into the June 8 bombing of a bus carrying policemen to work in the same district, which injured 15 people, Mutlu explained.

"The 19 suspects were handed over to the judicial authorities along with evidence that they were involved in the preparation stages of both attacks," he said.

Police believe the suspects are linked to "the terrorist organisation," he said, using the officialese for the armed separatist Kurdistan Workers' Party (PKK), listed as a terrorist group by Ankara and much of the international community.

Ten other people detained as part of the probe remain in police custody for questioning, he added.

Tuesday's attack and the June 8 blast were both claimed by the Kurdistan Freedom Falcons (TAK), an obscure radical group loyal to jailed PKK leader Abdullah Ocalan, sentenced for life in 1999.

The Turkish authorities say TAK is a front used by the PKK, especially when attacks claim civilian casualties.

The PKK has said TAK is a splinter group outside its control.

The rebels have dramatically stepped up attacks since Ocalan said through his lawyers last month he was abandoning efforts to seek dialogue with Ankara to peacefully end the 26-year Kurdish conflict.

The PKK threatened to spread the violence to urban areas after killing 12 soldiers in attacks in remote regions in the Kurdish-majority southeast at the weekend.

The group took up arms for self-rule in the southeast in 1984, sparking a conflict that has claimed some 45,000 lives.