JUNE 22 2010 17:05h
A radical Kurdish group claimed responsibility for the blast, which followed threats by the separatist Kurdistan Workers' Party (PKK) to spread violence to urban areas after a wave of bloody attacks on the army in the southeast.
Prime Minister Recep Tayyip Erdogan, under mounting criticism for mishandling the Kurdish problem, condemned the PKK, but insisted he remains committed to pledges to broaden the rights of the Kurdish community.
"The terrorist organisation knows very well that it will not get anywhere with such attacks... This is a dead end," he said in parliament.
The bus, carrying soldiers and their families, was passing through Halkali, a suburb on Istanbul's European side, when the bomb went off early Tuesday.
Istanbul Governor Huseyin Avni Mutlu said "it was a remote control bomb planted at the side of the road", adding that no suspect was immediately detained.
The blast killed three soldiers on their way to work as well as the 17-year-old daughter of an officer and wounded 12 people, two of them seriously, the governor said.
The death toll reached five later Tuesday when a soldier succumbed to his injuries in hospital, Anatolia news agency reported.
The Kurdistan Freedom Falcons (TAK) said in a statement they bombed the bus because Turkey "is planning a massacre of the Kurdish people" and has adopted "a concept of aggression" against jailed Kurdish rebel leader Abdullah Ocalan.
It threatened more violence, saying Ankara's policies "are forcing us to undertake even more intensive attacks."
Turkish officials say TAK is a front used by the PKK, listed as a terrorist group by Ankara and much of the international community, especially when attacks claim civilian casualties.
The PKK has said TAK is a splinter group outside its control.
The Turkish army meanwhile said seven PKK militants were killed in clashes overnight.
Five were shot dead after they attacked a gendarme station in southeast Turkey, killing one soldier. Two others were killed in a security operation in the northeast.
Fighting intensified at the weekend when PKK attacks claimed the lives of 12 soldiers, most of whom died when rebels assaulted a border unit at the Iraqi frontier, prompting a Turkish air raid on PKK rear bases in northern Iraq.
The PKK has dramatically stepped up violence since Ocalan, jailed for life in 1999, said through his lawyers last month he was abandoning efforts to seek dialogue with the government for a peaceful end to the 26-year conflict.
Ankara has rejected talks with the PKK though it has pledged to boost Kurdish freedoms and economic development in the southeast, hoping to discourage separatism and cajole the rebels into laying down arms.
The faltering initiative, announced last year, has met with public hostility amid persistent PKK violence, but Erdogan insisted Tuesday he remained committed to reform.
"We will not step back... We will not disappoint our (Kurdish) people once again," he said. "The terrorist organisation can never be the representative or the spokesman of our Kurdish citizens."
The PKK targets mainly the security forces but it has also carried out bomb attacks on civilians in the past.
In 2008, it was blamed for two explosions on a crowded street in Istanbul which killed 17 people and wounded more than 150.
In 2005, five people, among them Irish and British tourists, were killed when a PKK militant bombed a minibus in the Aegean resort of Kusadasi.
The PKK took up arms for self-rule in the mainly Kurdish southeast in 1984, sparking a conflict that has claimed some 45,000 lives.