The device was detonated as their bus passed on a road in the Karliova district of Bingol province, they said.

Sources blamed the attack on Kurdistan Workers' Party (PKK) militants.

Fighting between the army and PKK rebels in south-eastern Turkey has escalated in the past year, with hundreds of lives lost.

Nine officers were wounded in the blast on Sunday, Sept. 16 morning, the officials said.

The army has mounted scores of operations in that region, and in neighboring northern Iraq, in a bid to drive out the rebels.

The PKK has been fighting for an ethnic homeland in south-eastern Turkey since 1984. It is classified as a terrorist organization by Turkey, the U.S. and EU.

In all, more than 40,000 people have died in the conflict, according to BBC News.