OTTAWA - Canada's government on Thursday dismissed opposition demands for a public inquiry into claims that troops in Afghanistan handed detainees over to local officials who were believed to torture.

The main opposition parties made the demand after Richard Colvin, a Canadian diplomat stationed in Afghanistan at the time of the alleged abuse, told lawmakers there was a "likelihood" that Canadian forces broke international law.

Colvin maintained Canadian forces "detained, and handed over for severe torture, a lot of innocent people."

The number two in the Liberal Party, Bob Rae, has since demanded a public inquiry "to clear the air and clear the cloud over this government."

His call was backed by the leftist New Democratic Party and the independent Bloc Quebecois.

"You can't function, you can't restore the credibility of this great country internationally unless you hold a judicial public inquiry," Rae told reporters outside the House of Commons.

Bloc Quebecois chief Gilles Duceppe went further, saying that "if they (the Canadian government) knew what was going on, it's going against the Geneva Conventions, and this is a war crime."

The Conservative government of Prime Minister Stephen Harper has stood firm in the face of the withering attacks, rejecting any investigation.

"It's not acceptable," Defense Minister Peter MacKay said Thursday. "What I heard yesterday doesn't stand the test of cross examination, doesn't stand the test of credibility," he said of Colvin's testimony before a special parliamentary committee.

MacKay added that much of the evidence advanced by Colvin, now an intelligence liaison officer at the Canadian embassy in Washington, was hearsay.

"We're talking about basing much of his evidence on what the Taliban have been specifically instructed to lie about if captured," MacKay said.

Colvin worked for Canada's Foreign Affairs department in Kandahar in 2006 and was later promoted to second-in-command at the embassy in Kabul until late 2007.

In both jobs he visited detainees transferred by Canadian soldiers to Afghan prisons and reported his findings to Ottawa.

He claimed the warnings, first delivered in spring 2006, were ignored by senior military commanders and government officials, until prisoner mistreatment allegations were reported in the media a year later.

Colvin said he was eventually told to stop putting his reports into writing.

The Canadian government, which has some 2,800 troops in southeastern Afghanistan, has denied there is any firm evidence that detainees transferred by its officials were tortured.

Conservative members of parliament dismissed Colvin's testimony as not credible, saying it was based on second- and third-hand information, according to public broadcaster CBC.