The U.S. eavesdropping agency may be snooping on dozens of world leaders, but one intelligence expert says it's unlikely the National Security Agency is listening to Stephen Harper's calls.

Wesley Wark, a visiting professor at the University of Ottawa, points to an agreement among the so-called Five Eyes countries that they won't spy on one another.

"In a crisis, I think that convention might be temporarily suspended. But I don't think there's any crisis of that proportion that's come along in Stephen Harper's time," said Wark, who teaches in the university's graduate school of public and international affairs.

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The Five Eyes – Canada, the United States, Britain, Australia and New Zealand – have been exchanging information for decades and their signals intelligence agencies co-operate closely.

In addition, Wark says, the Canadian prime ministers' working style – controlled and discreet – makes him an unattractive target for U.S. spies.

"Harper wouldn't be a very interesting intelligence target for NSA, everything else aside, because he's not really a garrulous politician. He's quite the opposite."

British newspaper The Guardian – citing documents from whistleblower Edward Snowden – reports that the NSA monitored the phone conversations of 35 world leaders after being given their numbers by an official in another U.S. government agency.

Wark has no trouble believing such accusations.

"Clearly the NSA is doing this and has been doing it, against a range of world leaders, including some surprising figures," he said.

"I just don't see Canada on their radar screens."

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The prime minister's spokesman did not respond Friday to a request for comment.

Foreign Affairs Minister John Baird was coy when asked whether U.S. spies might be monitoring Canadian conversations about trade with the European Union or other matters of state.

"With respect to what the NSA does, I'll leave that for others."

Canada's eavesdropping agency, the Communications Security Establishment, says the Five Eyes do not target each other's citizens.

On the contrary, documents previously published by the Guardian indicate the NSA and Canada's CSEC teamed up with Britain's Government Communications Headquarters to monitor the computers and intercept the phone calls of foreign politicians and officials at two G20 summit meetings in London in 2009.

The paper said the efforts included penetration of delegates' BlackBerry smartphones to monitor their email messages and calls.

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It strongly suggests the fact Canadian politicians use the BlackBerry – and its highly touted security protocol – would not immunize them from foreign spies.

Wark says American intelligence has likely already dissected the device.

"I'm sure they took it apart completely, and the NSA would have access to it," he said. "Everything points to the extreme likelihood that they can get into BlackBerry."

But whether American spies are tapping into the handheld devices toted by Canadian cabinet members is another matter.

When Snowden, a former NSA contractor, began leaking materials to the media earlier this year, David Jacobson, then U.S. ambassador to Canada, was emphatic that the spy service wasn't training its mighty surveillance powers on its northern neighbour.

"The United States does not spy on Canadian citizens," Jacobson said.

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Some raise concerns about the reality that a good deal of Canadian Internet traffic is routed through the United States, providing potentially easy access to American intelligence.

Canadian privacy commissioner Jennifer Stoddart said in June she would look into any implications for Canada posed by the possible large-scale U.S. snooping exposed by Snowden.