The columnist with the Guardian newspaper was asked by the congressional committee about what role Canada played in obtaining information.
"They wanted to know specifically what information Canada collected about the ministry, what the objective of the spying was specifically, what exactly the methods that were used to collect this information and evade the system," Greenwald told the CBC's Susan Ormiston after testifying.
Former U.S. National Security Agency contractor Edward Snowden is the source of Greenwald's information, and the journalist told CBC News earlier this week that he has on Canada's alleged spying.
Brazil's politicians have expressed frustration at Canada's response to the allegations, and the senator leading an investigation into the matter pressured officials to explain.
"It's Canada's turn to come to Brazil to explain exactly what it's done against our country and what kind of espionage," Senator Vanessa Graziotin said. "And if it hasn't done anything, then tell us clearly that nothing has happened."
Click the video above for Susan Ormiston's report from Brazil.
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