Canada allowed the U.S. National Security Agency to spy on the 2010 G20 meeting in Toronto, according to a CBC report citing a leaked document from Edward Snowden.

On Wednesday evening, CBC reported it had obtained documents outlining "a six-day spying operation by the National Security Agency" that Canada had allowed to be run out of the U.S. embassy in Ottawa.

It is rare for one country to give any ally explicit permission to run spying operations on domestic soil. According to the CBC report, Canada did just that in giving a nod to the secret NSA operation to spy on G20 leaders.

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Asked about the allegations, a spokesman for Prime Minister Stephen Harper declined to detail what Canadian authorities knew.

"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," said Jason MacDonald, Mr. Harper's director of communications, in a written statement Wednesday evening.

The NSA is a very close counterpart of the Communications Security Establishment Canada, Ottawa's eavesdropping agency. A previous Snowden leak suggested that CSEC and the NSA assisted Britain's Government Communications Headquarters in spying on the previous G20 meeting, which was held in 2009 in London.

The NSA, GCHQ, and CSEC, and Australian and New Zealand counterpart agencies, have been running spying operations together since the end of the Second World War. Collectively, these agencies from English-speaking countries are known as the Five Eyes, and they agree not to spy on each other while spying on just about every other country.

Mr. Snowden is the former U.S. intelligence contractor who has leaked classified documents about NSA spying programs over the past six months – including disclosures that the NSA had been targeting mobile phones used by Germany's Angela Merkel and other world leaders. Taken together, the Snowden files have shown just how much the Five Eyes continues to be a real partnership and a highly aggressive one.

The Five Eyes have been known to publicly highlight their role in teaming up to fight Nazis, Soviets, and more, recently, al-Qaeda-affiliated terrorists, over the years. Yet the collective has been less forthcoming about its diplomatic and trade spying.

Yet such spying is routine, inside and outside of the Five Eyes. Diplomats who attend multilateral meetings are often cautioned to be very careful about guarding their communications and briefing books when they travel abroad.

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In 2000, Carleton University professor Martin Rudner, an expert in security matters, published an essay saying Canada's agency, CSEC, has long been after secrets during multilateral meetings and trade negotiation.

He wrote that "provided Canadian policy-makers and negotiators with economic intelligence pertaining to international trade negotiations, including the negotiations with Mexico on the North Atlantic Free Trade Agreement (NAFTA) of 1994; the 1995 multilateral ("Uruguay Round") trade negotiations; the Asia Pacific Economic Co-operation (APEC) Ministerial and Leaders' meetings in Vancouver in 1997," among other meetings.

In October, another Snowden leak showed that CSEC spied on telecommunications traffic affiliated with Brazil's Ministry of Mines and Energy last summer. The NSA had taken an interest in similar targets in Brazil at that time.

With a report from Josh Wingrove