"What happened yesterday (Sunday) has clearly shown who is close to who and who is in communication with who," Deputy Prime Minister Cemil Cicek told the Anatolia news agency.

"They have been caught red-handed," Cicek said, referring to the Democratic Society Party (DTP).

Three DTP lawmakers were present Sunday when the outlawed Kurdistan Workers' Party (PKK) handed over the eight soldiers to the Kurdish regional government in northern Iraq after holding them captive for nearly two weeks.

The chief prosecutor's office in Ankara on Monday launched an investigation to see if the involvement of the lawmakers -- Osman Ozcelik, Aysel Tugluk and Fatma Kurtulan -- constituted a crime under the anti-terror law, Anatolia said.

The investigation could lead to the lawmakers being formally charged.

The DTP, which has 20 seats in parliament, is frequently accused by Ankara of being a tool of the PKK, which took up arms in 1984 in a campaign for self-rule in Turkey's mainly Kurdish southeast. The conflict has claimed more than 37,000 lives.

The DTP rejects the charges and says it wants to see a peaceful resolution to the conflict.

The eight soldiers released on Sunday were captured by the PKK on October 21 during a bloody ambush on a military unit near the border with Iraq, that also left 12 other soldiers dead.

The attack raised regional tensions and put pressure on the Turkish government to launch military strikes in northern Iraq to root out PKK rebels using the region as a springboard for attacks across the border in Turkey.

Ankara accuses Iraqi Kurds of supporting the group, listed as a terrorist organization by much of the international community.

Turkish Prime Minister Recep Tayyip Erdogan is set to hold a crucial meeting with US President George W. Bush later Monday in Washington that many expect will be pivotal in determining Ankara's next course of action.