The suspects, eight of them women, were arrested at a border post in Sirnak province after they crossed into Turkey from Iraq, the local governor's office said on its web site.

Members of the separatist Kurdistan Workers' Party (PKK), including senior commanders, have taken refuge in northern Iraq and Ankara said Tuesday it would order a cross-border operation to crack down on PKK bases there "if necessary."

Police learnt that the 20 suspects met PKK commanders in northern Iraq and were ordered to set up a "new structure" of disobedience against Ankara in the predominantly Kurdish southeast, the statement said.

"It was understood that they were given orders to... create an atmosphere of chaos among the people and prepare for acts against state institutions," it said.

The suspects were instructed to continue spreading allegations that PKK leader Abdullah Ocalan, serving a life sentence on a prison island in northwest Turkey since 1999, is being sytematically poisoned.

Turkish prosecutors investgated the allegations by Ocalan's lawyers earlier this year and said toxicology tests showed the claims were "totally groundless."

Most of the suspects are university students, the Anatolia news agency reported and are expected to appear before a judge who will decide whether to charge them or free them.

The PKK, listed as a terrorist group by Ankara and much of the international community, launched a bloody campaign for Kurdish self-rule in the southeast in 1984. The conflict has claimed more than 37,000 lives.