Prime Minister Stephen Harper continued to defend his decision not to release a report on the Middle East by Conservative MP Wajid Khan, saying there's no precedent to do so.

During question period Thursday, Liberal Leader Stéphane Dion pressed Harper to make the report public, adding that there must be "something there that the prime minister does not want to release to the Canadian people."

The Liberals have been trying to get Khan to appear before the foreign affairs committee, of which he is a member, to speak about his report.

Khan was sitting as a Liberal when he agreed in the summer of 2006 to act as a special adviser on the Mideast to Harper. Khan promised at the time that his report would be available to all political parties, promising it would be "unbiased and freestanding."

Khan, who represents the Ontario riding of Mississauga-Streetsville, jumped to the Conservatives last month. His mission took him to Syria, Jordan, Saudi Arabia, Egypt, Israel and Lebanon in September 2006.

The Prime Minister's Office has since said his report would not be released to the public, saying that would make Khan a pundit and not an adviser.

Harper told Dion that "special advisers to the prime minister don't release their reports publicly. They haven't in the past. They won't be in the future."

"If he was interested in the opinions of the honourable member of Mississauga-Streetsville he had three years to ask him those opinions and never did so," Harper said.

Not easy to get MP to testify

Bryon Wilfert, the Liberal foreign affairs critic, had suggested that Khan should be subpoenaed to the foreign affairs committee.

But as the CBC's Susan Bonner reports, a member of Parliament can only be compelled to testify before a committee if a motion has been passed in the House of Commons.

"That can be tricky for precedent reasons," Bonner said.

Opposition MPs have also questioned the credentials of Khan to be an adviser.

Khan, a Muslim and former pilot and officer in Pakistan's military, is a successful car dealer in the Toronto area. He said he was moved to offer his help to Harper after police moved to end an alleged terrorist plot in Toronto.

Khan previously explained that he got the assignment because he has "some expertise … I have contacts and I have intel."