OTTAWA - The Conservative government's decision to appoint a retired judge to rule on documents related to Afghanistan detainees does not go far enough, Liberal Leader Michael Ignatieff said Monday.

In an open letter to Prime Minister Stephen Harper, Ignatieff said the appointment of retired justice Frank Iacobucci to advise on the matter is an "overdue admission that action must be taken."

Iacobucci's reputation is beyond reproach, Ignatieff wrote, but his mandate, his deadline and his responsibilities are unclear.

Iacobucci cannot do his job adequately unless the government gives him the mandate to hold a full public inquiry, Ignatieff said. Anything less won't provide the answers to which Canadians are entitled.

"A public inquiry would give him the power to demand materials from the government, to call witnesses and to subpoena testimony," Ignatieff wrote.

"An inquiry could establish the facts and make recommendations for the future."

Justice Minister Rob Nicholson moved Friday to avert a collision over whether MPs should be allowed to see classified detainee documents by appointing Iacobucci to advise on what may be released.

The New Democrats have dismissed the decision as delay tactic that sidesteps the core issue: Parliament's right to see whatever documents it wants.

The House of Commons voted Dec. 1 to force the release of documents outlining what the government knew about the risks of torture for prisoners captured by Canadian soldiers and handed over to Afghan authorities in 2006-07.

A special committee of MPs was told last fall that the risks were clear at the time, but prisoners were still handed over for months before a new policy was introduced in 2007 giving Canada the right to monitor Afghan jail conditions.

Opposition MPs said they had a right to the documents, but the government countered that the material was sensitive and had to be protected because of national security.

"The Afghan detainee scandal is about much more than the government's refusal to hand over to Parliament and the Canadian people the documents they need in order to get to the bottom of this sorry affair," Ignatieff wrote.

"It is about the government's handling of the detainee issue from the beginning."

Liberal MP Derek Lee has threatened to bring a motion to hold the government in contempt of Parliament over the documents.

Handing the issue to former judge may have delayed a showdown in the Commons for now, but conflict and debate over the controversy continues.

The NDP said it would give the government until March 19 to comply with the parliamentary vote before bringing its own contempt motion.

Said Ignatieff: "Detainee transfer is sure to remain an issue of importance for future Canadian missions overseas, and it is vital that Parliament and Canadians learn from the mistakes of the past in order to prevent them from happening again."

Iacobucci is a former law professor and deputy justice minister who served on the high court from 1991 to 2005. He recently completed an inquiry into the overseas torture of three Arab-Canadians.