"The accusations must be immediately investigated," said SPD defense expert Rainer Arnold on Thursday.

Both partners in Germany's coalition government have agreed to investigate claims made by the German-born Turk that he had been physically mistreated by troops from the special operations KSK unit of the German army, the Bundeswehr.

While the government has confirmed that that KSK soldiers had been in touch with Murnaz, a defense ministry official said Wednesday that they had "verbal contact" with him in a US detention center in Afghanistan, but there was no proof to back up his claims he was physically abused.

Murat Kurnaz, 24, was released in August after spending four years from the US military jail in Guantanamo Bay.

US investigators had claimed he was an Islamist "enemy combatant" with links to terrorist organization al Qaeda.

Verbal contact only

Defense ministry officials revealed that 69 soldiers had been questioned about the incident.

From the replies of a handful of soldiers it had been established that after Kurnaz's arrest in Pakistan in 2001, German forces were alerted by their US counterparts that one of the detainees spoke German.

One of the German soldiers allegedly told Kurnaz: "You were on the wrong side."

But there was no evidence to suggest any further contact between the soldiers and Kurnaz, the spokesman said.

Unanswered questions

German prosecutors on Tuesday dropped a long-running investigation into Kurnaz after saying they had found no firm proof that he had belonged to a terrorist organization.

The parliamentary committee is likely to take a fresh look at Foreign Minister Frank-Walter Steinmeier's role in the case, as well as hearing evidence from then-Defense Minister Rudolf Scharping (SPD) and Kurnaz himself.