Brazil said Monday Washington had not sufficiently responded to Brasilia's request it explain the alleged US electronic spying disclosed by rogue intelligence leaker Edward Snowden.
"Some clarifications were made; we view them as insufficient," Foreign Minister Antonio Patriota said at a joint press conference with his Nigerian counterpart Olugbenga Ayodeji Ashiru.
Patriota said there had basically been nothing new since his appearance before Congress last week, when he said he was awaiting a formal response from Washington.
Brasilia set up a technical group made up of representatives of the ministries of justice, defense, foreign affairs, science and technology as well as security experts to deal with the issue, the foreign minister added.
Last week the daily O Globo newspaper published a series of reports on US electronic espionage operations in Brazil and Latin America, based on documents leaked by Snowden, a US former National Security Agency (NSA) contractor.
The newspaper said the NSA spied on Brazilian residents and companies, as well as people traveling in Brazil.
Washington also maintained a base in Brasilia to intercept foreign satellite communications, it added.
The daily also published an NSA document dated September 2010 which seemed to indicate the Brazilian embassy in Washington and the Brazilian mission to the UN in New York were targeted by the agency.
President Dilma Rousseff ordered federal agencies to investigate the reports and stressed that, if substantiated, they would constitute a "violation of (our) sovereignty."
The 30-year-old Snowden has applied for asylum in 27 countries as he tries to evade American justice for disclosing a vast program of US worldwide electronic surveillance.
Snowden, whose passport has been revoked by Washington, has been marooned in Moscow airport's transit zone for the past three weeks.
In a sign that Moscow may seriously consider an application from him, speaker of the lower house of parliament Sergei Naryshkin said Friday Snowden could apply for either temporary asylum or political asylum.
The US fugitive has so far only won a sympathetic ear from some leftist Latin American countries, including Venezuela.