The suspects are believed to be members of the separatist Kurdistan Workers' Party (PKK), which has waged a bloody 23-year campaign for self-rule in the area, police said.

The police believe they were planning to bomb the train station in Diyarbakir, the region's largest city, which the army uses extensively to ferry soldiers and military equipment.

In a separate development, a soldier was killed Thursday in clashes with PKK militants in the mountains in Sirnak province near the Iraqi border, security sources said, adding that the violence was continuing.

Since last year, the army has stepped up action against the PKK, conducting several air raids and a week-long ground offensive against rebel bases in northern Iraq.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms in 1984, sparking a conflict that has claimed more than 37,000 lives.