Eight Turkish troops captured and then freed by Kurdish rebels are being held in a military jail and face unspecified charges, army sources say.
The soldiers have been criticised by some in Turkey, amid allegations that they acted as cowards and fostered Kurdish propaganda.
The troops, who were captured on 21 October in an ambush that killed 12 other soldiers, were freed last Sunday.
Kurdish rebels have killed 40 soldiers and civilians in the past month.
Dozens of rebels have also been killed over the same period, Turkey's military says, as the Kurdistan Workers' Party (PKK) stepped up its attacks.
The PKK - which is treated as a terrorist organisation by Turkey, the EU and US - has waged a violent campaign for a Kurdish homeland since 1984, resulting in more than 30,000 deaths.
There are no clear indications of the charges the soldiers face although one lawyer involved in the case told Associated Press news agency they included disobedience and escaping abroad.
The lawyer said the soldiers were in a military prison in the eastern province of Van.
Criticism of the troops' actions had even come from Justice Minister Mehmet Ali Sahin.
"No member of the Turkish armed forces should have found themselves in such a situation," he said last week.
"As a Turkish citizen I cannot accept the fact that they went with the terrorists that night. Our soldier is prepared to die if necessary when he is protecting the country."
An investigation is under way into the release of the troops, which came ahead of a key meeting between Turkish Prime Minister Recep Tayyip Erdogan and US President George W Bush.
The investigation will include the role of three lawmakers from Turkey's pro-Kurdish Democratic Society Party who went to northern Iraq to take part in the release ceremony with Iraqi officials.
The deadly ambush brought the Kurdish rebel situation to a head.
Turkey has amassed about 100,000 troops on the Iraqi border and has threatened to make cross-border incursions to deal with the rebels.
Turkey's Western allies and Iraq have urged it to show restraint. ( BBC )