(Adds CSE watchdog says it reviewing agency use of data, comments by privacy commissioner's office and Brazil government)
By David Ljunggren and Mike De Souza
OTTAWA, Jan 28 (Reuters) - Canada's electronic spy agency has been intercepting and analyzing data on up to 15 million file downloads daily as part of a global surveillance program, according to a report published on Wednesday.
Critics said the revelations, made in 2012 documents obtained by former U.S. spy agency contractor Edward Snowden and leaked to journalists, showed much more oversight was needed over Canada's Communications Security Establishment (CSE).
The documents are the first indication from the Snowden files showing Canada had its own globe-spanning Internet surveillance in a bid to counter extremists.
The covert dragnet, nicknamed Levitation, has covered allied countries and trading partners such as the United States, Britain, Brazil, Germany, Spain and Portugal, the report by CBC News and news website The Intercept said. The Intercept, which includes journalist Glenn Greenwald, obtained the documents from Snowden.
Brazil's government, which fell out with Washington in 2013 over revelations that the U.S. National Security Agency, Snowden's former employer, had eavesdropped on President Dilma Roussef, criticized the reported Canadian spying.
"Brazil regrets and repudiates all unauthorized espionage on foreign officials by intelligence agencies," the Foreign Ministry said in a statement emailed to Reuters on Wednesday. It said Brazil has sought to enhance Internet privacy and security through international governance agreements.
A U.S. intelligence official declined to comment.
The Canadian Broadcasting Corporation News (CBC) report said the CSE nets what it said the agency calls 350 "interesting download events" each month.
CSE is a secretive body, which like the NSA, monitors electronic communication and helps protect national computer networks. It is not allowed to target Canadians or Canadian corporations.
In the past, CSE has faced allegations that it has improperly intercepted Canadians' phone conversations and emails. CSE says it has safeguards in place to protect any information about Canadians it might inadvertently collect.
An independent watchdog monitors CSE, but the watchdog's powers are limited. A spokesman said it is reviewing CSE's use of metadata but declined to say if it would include the latest reports in the process.
Opposition parties moved in Parliament last October to give the CSE watchdog a more robust role but were defeated by the governing Conservatives.
Among CSE's hauls, the eavesdropping program has discovered a German hostage video and an uploaded document that revealed the hostage strategy of an al-Qaeda wing in North Africa, the CBC said.
The agency did not confirm the report, saying in a statement that "CSE's foreign signals intelligence has played a vital role in uncovering foreign-based extremists' efforts to attract, radicalize, and train individuals to carry out attacks."
The Snowden documents show the agency has sifted through 10 million to 15 million uploads a day of videos, music documents and other files hosted by 102 file-sharing websites.
Canada is part of the Five Eyes intelligence sharing network, along with the United States, Britain, Australia and New Zealand.
In 2013, Brazil's Rousseff demanded an explanation from Canada after a media report, also based on Snowden documents, said CSE spied on the South American country's mines and energy ministry.
Canadian security expert Wesley Wark said Levitation might well be covered by CSE's foreign intelligence mandate, but questioned its effectiveness.
"Does this massive trawling of free download sites aimed at detecting terrorist communications or identities really deliver useful intelligence?" asked Wark, a University of Ottawa professor, noting CSE had talked of only two successes.
In 2013, the CBC cited other Snowden documents that it said showed Canada had allowed the NSA to conduct widespread surveillance during the 2010 Group of 20 summit in Toronto.
Last August, the government watchdog said CSE should tighten its procedures for handling the private calls and emails it intercepts.
"These are powerful capabilities in the hands of the state that in effect monitor all of our digital actions," said Ron Deibert, director of the Canada Center for Global Security Studies. "They collect it all; are we confident that they are not going to abuse it?" (Additional reporting by Alastair Sharp in Toronto, Anthony Boadle in Brasilia, Mark Hosenball in Washington; Editing by Amran Abocar, Peter Galloway, Dan Grebler and Grant McCool)