CBC News has released a top-secret document retrieved by U.S. whistleblower Edward Snowden showing the Canadian government allowed the largest American spy agency to conduct widespread surveillance in Canada during the 2010 G8 and G20 summits.

The four-page National Security Agency document was posted online at CBC.ca early Monday.

The document is one of thousands that Snowden entrusted to U.S. freelance journalist Glenn Greenwald, who co-authored the story reported exclusively by CBC News on Nov. 27.

Since then, CBC has offered the U.S. government an opportunity to retrieve and review the document from its files, and to comment on any information in the document it believes should not be released.

David Walmsley, CBC's director of news content, says the public broadcaster "believes in transparency to support its journalism."

Late Sunday, the NSA requested only that CBC News black out any information that could identify NSA and other U.S. government employees to protect their personal safety.

The network agreed with the request, and certain segments of the documents appearing online have been blacked out.

The U.S. State Department initially issued a statement in reaction to the original CBC story about the NSA's spying at the G20 summit, pointing out U.S. President Barack Obama has already ordered a broad review of U.S. intelligence activities in the wake of Snowden's earlier revelations.

But on Friday, a State Department official said there would be no comment on the publication of the actual secret document: "Thank you for the offer, but we cannot discuss allegedly classified materials."

Later Friday evening, the White House requested an opportunity to review the document. An official sent CBC an email Sunday morning, saying: "We are not going to comment publicly on every specific alleged intelligence activity."

Questions remain

Wesley Wark, one of Canada's leading experts on national security and intelligence, reviewed the document and says it still leaves a lot of questions.

The biggest, he says, is Canada's role in the NSA's surveillance operations at the G8 and G20.

The document says only that the NSA's surveillance plans were "closely co-ordinated with the Canadian partner" — the Communications Security Establishment Canada (CSEC).

Both agencies gather intelligence by intercepting phone calls and data, and by hacking into computer systems.

But Wark says it is not clear from the document what the NSA was "co-ordinating" with Canada before and during the Toronto summit.

"This may be commonplace and relatively banal or it may be very troubling," Wark said in an interview. "But until we have more of this story, I don't think we know where it goes."

Both the U.S. and Canadian governments have refused to provide any details of security and intelligence operations during the summits.

"I don't think we can accept at face value the assurances of the government about the legal mandate of CSEC," Wark says. "Nor can we simply assume that something illegal happened here. We just don't know enough from my perspective."

While much of the U.S. intelligence gathering during the summit was related to security, the document also talks about snooping operations in support of policymakers.

"They would want to be collecting intelligence on the sort of personalities of key international leaders — often you get some very interesting information from these kinds of summit meetings, where they are close in with conversations and chit-chats among delegates in not always secure circumstances," Wark says.

"They would want some political intelligence whatever (way) they could acquire it, and some economic intelligence.

"So there might be a whole range of things, and the document itself refers to various tasks that exist for the NSA [at the G20] in terms of that policy support."