The relatively low-key surveillance was reported by the Folha de S. Paulo newspaper, based on Brazilian intelligence service documents it obtained from an undisclosed source.
It describes surveillance that pales in comparison to the massive spy programs carried out by the U.S. National Security Agency, efforts detailed in thousands of documents leaked by Edward Snowden.
But the revelation forced the Brazilian government to defend its espionage while remaining the loudest critic of the NSA programs that have aggressively targeted communications in Brazil, including the personal phone and email of President Dilma Rousseff, who cancelled a state visit to Washington in response.
Brazil's Institutional Security Cabinet, which oversees the Abin intelligence service, said in an emailed statement that all the operations cited in the Folha report "follow Brazilian law for the protection of national interests."
The statement added that Abin "develops intelligence activities for the defense" of Brazil and for "national sovereignty, in strict observance of constitutional principles and the laws that guarantee individual rights."
Rousseff has said that the NSA program, which has swept up data on billions of telephone calls and emails flowing through Brazil, is a violation of individual human rights. Brazil has been targeted in part because it serves as an important transit point for trans-Atlantic fiber optic cables carrying much of the globe's traffic.
Last week, Brazil joined Germany in asking the United Nations General Assembly to adopt a resolution calling on all countries to protect the right to privacy guaranteed under international law. The draft emphasizes that illegal surveillance and interception of communications as well as the illegal collection of personal data "constitute a highly intrusive act that violates the right to privacy and freedom of expression and may threaten the foundations of a democratic society."
In Monday's statement, Brazil's Institutional Security Cabinet said it planned to prosecute anyone who may have leaked the documents to the Folha newspaper.
According to daily, Brazil's intelligence service monitored office space rented by the U.S. Embassy in Brasilia, suspecting it of harboring spy equipment. The report said Abin had concluded that the offices held "communications equipment."
"Functioning daily with the doors closed and the lights turned off, and with nobody in the locale," is how the Abin report described the rented U.S. property, according to Folha. "The office is sporadically visited by someone from the embassy."
Dean Cheves, the spokesman for the U.S. Embassy in Brazil, wouldn't comment on Abin's surveillance of the office space. But he said the office served as a relay station for walkie-talkie radios carried by embassy personnel, who carry the radios as back up communications for emergencies or in case cellphone service goes down.
The Folha report detailed at least 10 intelligence operations carried out in Brasilia in 2003-04, just as former President Luiz Inacio Lula da Silva was settling into office.
Other targets included diplomats from the Russian, Iranian and Iraqi embassies, who were followed and photographed as they came and went from embassies and official residences.
In particular, Abin was interested in Russian officials involved in negotiating arms deals in Brazil, and followed Iran's ambassador to Cuba as he visited Brazil.
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