By David Ljunggren

OTTAWA (Reuters) - The Canadian government came under pressure on Thursday to investigate allegations that senior officials ignored evidence that Afghan authorities were torturing detainees handed over by Canadian troops.

In bombshell testimony on Wednesday, diplomat Richard Colvin said Canada's detainee practices in 2006 and 2007 were "probably illegal" and said his superiors had tried to shut him up when he raised the alarm.

"The only way to get to the bottom of Richard Colvin's explosive revelations is a full public inquiry," said Paul Dewar, a legislator with the left-leaning opposition New Democratic Party.

Canada has 2,700 soldiers in the southern Afghan city of Kandahar on a combat mission that is due to end in 2011.

The furor comes at a time when Canadians show signs they are tiring of the mission. So far 133 soldiers have died.

Colvin -- who was based in Afghanistan for most of 2006 and 2007 -- sent a total of 17 reports to senior Foreign Ministry and National Defense officials, laying out his concerns that prisoners handed over to Afghan authorities by Canadian troops were being abused.

Government ministers insist they were not made aware of any of the reports.

Colvin made his comments in testimony to a House of Commons committee on Afghanistan, where members of the Conservative government suggested he had been duped by Taliban members lying about being tortured.

"All of this information, all of the things he told us ... (were) second-hand at best. They came from people who are trained to lie, frankly, that's their mantra," said Laurie Hawn, parliamentary secretary to Defense Minister Peter MacKay.

Hawn told CTV television on Thursday that it was easy to make allegations "or run around with your hair on fire".

Canadian troops first began transferring detainees to Afghan authorities in late 2005. Eventually, faced with persistent stories and allegations of abuse, Ottawa signed a deal with Kabul in May 2007 to increase protection for detainees.

Colvin, who alleged the abuses had continued even after that agreement was signed, said many Afghans arrested by the Canadian military were innocent.

MacKay blasted opposition legislators last month after they raised the issue of abuse, saying they were more interested in the rights of Taliban members than in Canada's troops. Prime Minister Stephen Harper used the same line in 2007.

Ottawa University law professor Amir Attaran said the onus was on MacKay to explain how he could not have known about Colvin's reports. At the time, MacKay was foreign minister.

"How could he avoid seeing something that ... his top civilian on the ground in Afghanistan, on 17 occasions, told him was a problem?" Attaran told CTV.

Foreign Minister Lawrence Cannon said the government had acted when it received specific allegations of abuse.

"Nothing has been proven here," he told reporters on a conference call from Kabul, referring to Colvin's comments.

Asked whether Ottawa would probe the allegations, a spokeswoman for Cannon said the government would let the House of Commons committee on Afghanistan continue its work.

"What are they (the government) going to say? 'No, we don't want to get to the bottom of this,' and just leave this hanging? There's a cloud right now over Canada's reputation," the NDP's Dewar told reporters.

(Reporting by David Ljunggren; editing by Rob Wilson)