Canada let the US spy agency conduct widespread surveillance during the G8 and G20 summits in Toronto in 2010, according to documents leaked by Edward Snowden, the former US National Security Agency contractor and whistleblower.
Reported exclusively by the Canadian Broadcasting Corporation on Wednesday, the documents reveal that American officials turned the US embassy in Ottawa into a security command post during a six-day, NSA spying operation as US President Barack Obama and other world leaders met in June 2010.
The CBC report said the documents did not reveal the precise targets of the NSA operation, but described part of the US mandate during the Toronto summits as "providing support to policymakers".
The spying operation was reportedly "closely coordinated with the Canadian partner", according to a leaked NSA briefing note.
A spokesperson for Stephen Harper, Canadian prime minister, declined to comment on Wednesday on the report's allegations.
"We do not comment on operational matters related to national security," spokesperson Jason MacDonald said.
A spokeswoman for Canada's equivalent of the NSA, the Communications Security Establishment Canada (CSEC), said they could not comment on the operations of Canada or its allies.
"Under the law, CSEC does not target Canadians anywhere or any person in Canada through its foreign intelligence activities,'' Lauri Sullivan, spokesperson, said.
"CSEC cannot ask our international partners to act in a way that circumvents Canadian laws."
OpenMedia.ca, a Canadian civil liberties group, condemned the spying.
"It's... clear this spying was aimed at supporting US policy goals during a highly contentious summit," Steve Anderson, the group's executive director, said in a statement.
"This is sure to cause huge damage to Canada's relationships with our other G20 partners."
Harper came under fire last month after a report by a Brazilian broadcaster alleged the CSEC spied on a Brazilian government ministry, straining ties between the two countries.
Snowden began leaking top-secret documents detailing the NSA's collection of millions of US communications records earlier this year.
Reports coming out of the leaked materials allege the NSA monitored German Chancellor Angela Merkel's mobile phone, scanned millions of French telephone records, and hacked the computer network of Brazil's state-run oil company, Petrobras.