By Murray Brewster, The Canadian Press

OTTAWA - The federal government is blocking whistleblowing diplomat Richard Colvin from giving documents to a special House of Commons committee investigating Afghan torture.

The revelation Wednesday came one day after Prime Minister Stephen Harper pledged that the committee would get "all legally-available" documents in order to carry out its investigation.

Justice Department lawyers have told Colvin - through the Foreign Affairs Department - that they do not accept the view that testimony before Parliament is exempt from national security provisions of the Canada Evidence Act.

As a result, Colvin's lawyer has written to the committee advising that Colvin won't be able to provide documents to Parliament as he was instructed to do last week.

Given "the potentially grave repercussions to Mr. Colvin for violating provisions of the Canada Evidence Act, Mr. Colvin is not now in a position to comply with the committee's request for documents without further instruction resolution of the question of the applicability of (Section) 38 to the documents," Lori Bokenfohr wrote in a letter obtained by The Canadian Press.

Violating Section 38 of the Canada Evidence Act can be punishable by five years in prison.

Defence Minister Peter MacKay said the government intends to comply with the order to produce documents, but tempered expectations by saying the records will pass through several filters before they get to MPs.

"Anything we're legally required to hand over, we'll hand over," he said Wednesday.

"We have to, of course, respect the Canada Evidence Act, The National Defence Act and rules pertaining to disclosure. And of course anything having to do with national security will have to be vetted."

Those are the same arguments the government made to the Military Police Complaints Commission, whose public hearings into the same issue were derailed by legal wrangling. The government took a year to censor and hand over records to the watchdog agency and at one point stopped releasing documents entirely.

MacKay did not explain how the Justice Department could ignore Parliament's authority when it comes to providing evidence.

Bokenfohr's letter said that government even considers testimony given to MPs behind closed doors to be subject to the blanket of national security.

NDP defence critic Jack Harris said the promise of openness wasn't even 24 hours old before it was broken.

Opposition MPs had been demanding to see a series of documents referenced by Colvin before they hear from David Mulroney, a senior official on the Afghan file who is now ambassador to China.

Harris said the only way to clear up the contradiction is for a full-blown public inquiry.

"In a commission of inquiry, nobody would push around a justice," he said. "There would be a documentary trail established and witnesses would be called to speak to those documents."

Colvin gave politically explosive testimony last week, alleging that all prisoners Canada handed over to Afghan authorities were likely tortured in 2006 and early 2007.

Before hearings into the controversy got underway, the Liberals asked for an opinion from Parliament's law clerk about how much could be aired in public.

The clerk advised that parliamentary immunity covers almost all of what's said.

But just days before his testimony, Justice Department lawyers warned Colvin in writing that they disagree and that he was to conduct himself "according to the interpretation" of the Canadian government.

Bokenfohr's letter also says that some of Colvin's reports were copied to the foreign minister's office - something MacKay, who was in that portfolio at the time, conceded in interviews last week and restated again Wednesday.