The allegations were published on Saturday by O Globo newspaper.
They were based on documents disclosed by fugitive American intelligence analyst Edward Snowden.
Brazil received the reports “with deep concern,” Foreign Minister Antonio Patriota said in a statement.
President Dilma Rousseff called several cabinet ministers to a meeting on Sunday to discuss the issue, following the publication of the newspaper articles on Saturday.
Mr Patriota was taking part in an international literature meeting in the city of Paraty, near Rio de Janeiro, but called the media in the afternoon to read a statement.