Three suspected members of the outlawed Kurdistan Workers' Party (PKK), which carried out last week's assault, were charged with membership in an illegal organisation and carrying out armed attacks on its behalf.

The two remaining suspects were charged with aiding and abetting.

Police are still questioning a sixth suspect and also looking for the alleged mastermind of the attack in Diyarbakir, the main city in Turkey's mainly Kurdish southeast.

Two other people were released without charges after being questioned by police.

At the weekend, the PKK claimed responsibility for Wednesday's attack in which the assailants, armed with machine guns, opened fire on a bus carrying employees of the local police academy.

The attack coincided with a parliamentary vote extending the government's mandate to order strikes against PKK hideouts in northern Iraq.

The army has stepped up operations against the PKK -- both inside Turkey and in northern Iraq -- since October 3 when rebels assaulted a Turkish border outpost near the border, killing 17 soldiers.

The PKK, listed as a terrorist group by Ankara and much of the international community, took up arms for Kurdish self-rule in the southeast in 1984. The conflict has claimed some 44,000 lives.