-report@ (Adds reaction, background, changes dateline from TORONTO)
OTTAWA, Nov 28 (Reuters) - Canada allowed the U.S. National Security Agency to conduct widespread surveillance during the 2010 Group of 20 summit in Toronto, according to a Canadian Broadcasting Corp report that cited documents from former NSA contractor Edward Snowden.
The report is the latest potential embarrassment for the NSA as a result of Snowden's leaks. He has already revealed the agency spied on close allies such as Germany and Brazil, prompting heated diplomatic spats with Washington.
The CBC report, first aired late on Wednesday, cited briefing notes it said showed the United States turned its Ottawa embassy into a security command post during a six-day spying operation by the top-secret U.S. agency as President Barack Obama and other world leaders met that June.
Reuters has not seen the documents and cannot verify their authenticity.
The CBC report said the operation was no secret to Canadian authorities. It said an NSA briefing note described the operation as "closely coordinated with the Canadian partner".
The Canadian equivalent of the NSA is the Communications Security Establishment Canada, or CSEC. Last month Brazil angrily demanded an explanation for media reports which said CSEC agents had targeted its mines and energy industry.
The CBC report said the documents did not reveal the precise targets of the NSA operation, but described part of the U.S. eavesdropping agency's mandate at the Toronto summit as "providing support to policymakers".
A spokesman for Canadian Prime Minister Stephen Harper declined to comment on the allegations in the report, but said security organizations were subject to oversight.
"We do not comment on operational matters related to national security. Our security organizations have independent oversight mechanisms to ensure that they fulfill their mandate in accordance with the law," Jason MacDonald said in an email to Reuters.
CSEC spokeswoman Lauri Sullivan, asked whether the CBC report was accurate, said the agency did not target anyone in Canada through its foreign intelligence activities.
"CSEC cannot ask our international partners to act in a way that circumvents Canadian laws," she added.
CSEC, which has a very low public profile, employs about 2,000 people. It is part of the so-called Five Eyes intelligence-sharing network that also includes the United States, Britain, New Zealand and Australia.
CSEC head John Forster had already been scheduled to appear later on Thursday before the House of Commons defense committee to discuss the annual budget for the defense ministry, which has overall responsibility for the agency.
After the allegations that CSEC had spied on Brazil, the British Columbia Civil Liberties Association and the OpenMedia.ca lobby group announced a lawsuit last month alleging such activities were illegal and unconstitutional.
OpenMedia.ca executive director Steve Anderson said Canadians watching the CBC report would "be shocked to discover just how secretive, expensive, and out-of-control our government's spying activities are".
He added in a statement: "This is sure to cause huge damage to Canada's relationships with our other G-20 partners."
The U.S. embassy in Ottawa was closed for the Thanksgiving holiday on Thursday.
(Editing by Jeffrey Hodgson and David Brunnstrom)