Four people have been killed and 12 others wounded in a bomb attack on a bus carrying military personnel and their families in Turkey's largest city, Istanbul.

The remote-controlled roadside bomb was detonated close to a military housing complex on Tuesday morning.

Three of those killed were army soldiers, while the fourth was a 17-year-old girl, Turkey's state news agency Anatolian reported.

Local TV showed images of the heavily damaged bus, which was part of a convoy of three buses passing through the Halkali district, a suburb on the European side of the city.

"According to initial information, it was a remote-control bomb planted at the roadside," Huseyin Avni Mutlu, Istanbul's provincial governor said.

"This is a terrorist attack, and the aim of the attack is clear - to create divisions, tensions and despair."

PKK warning

Al Jazeera's Anita McNaught, reporting from Istanbul, said that the attack took place on an open road on the far outskirts of the city, away from any habitation.

No group immediately claimed responsibility for the attack, but our correspondent said the bombing shows the hallmarks of the Kurdistan Workers Party (PKK) attacks, which have been growing in number since the beginning of June.

She said that the PKK had warned that it would "take the fight to the cities" after 12 of its fighters were killed in clashes with Turkish soldiers on Saturday.

At least a dozen soldiers have died in the recent upsurgeof violence.

The bombing of the bus comes a day after Turkish military forces began a major deployment along the border with Iraq.

Our correspondent said that about two weeks ago there was a similar attack on a police bus, with only minor injuries, on the western outskirts of Istanbul.

Escalating conflict

Fighting has escalated in the southeast of Turkey, which is predominantly Kurdish, in recent weeks.

It follows increased infiltration by PKK members into Turkeyfrom the mountains of northern Iraq where thousands of the fighters are based.

The increase in confrontations in recent weeks came after the PKK called off a year-old unilateral ceasefire and announced it was resuming attacks on Turkish forces.

The group accuses the military of offensive attacks and the government of impeding a political resolution of the conflict.

More than 40,000 people, mostly Kurds, have been killed in violence since the PKK launched its armed struggle against the Turkish state in 1984.

PHOTO CAPTION

Forensic officers work at the scene of a bomb blast in Istanbul June 22, 2010.

Al-Jazeera