The US government spied on Brazilian state-run oil giant Petrobras, according to intelligence documents released Sunday by Globo television.
Globo said it obtained the information from Glenn Greenwald, a blogger and columnist for the Guardian newspaper, who got secret files from US National Security Agency leaker Edward Snowden.
No details were immediately available about the nature of the spying, other than that the information was based on documents dated June 2012.
Globo said it was unaware of the scope or objectives of the spying on Petrobras, which is the world's leader in deep-water oil exploration and has an annual turnover of 200 billion reais (about $90 billion).
A week ago, the network reported that the NSA had intercepted communication from Brazilian President Dilma Rousseff and from Mexican President Enrique Pena Nieto. That story was also based on information from Greenwald.
Rousseff, who is scheduled to visit Washington on October 23, warned that she would cancel the trip if she did not get convincing explanations from the Obama administration.
Obama has vowed to ease tensions with Rousseff and Pena Nieto, telling them in separate meetings at last week's G20 summit that he understood their reaction.
The US president has vowed to provide answers by Wednesday.
Greenwald, who is based in Rio de Janeiro, said the NSA was using a program to access all Internet content Rousseff visited online in order to better understand her methods of communication and interlocutors.
The NSA program allegedly allowed agents to access the entire communications network of the president and her staff, including telephone, Internet and social network exchanges.
Some of Pena Nieto's email, phone calls and text messages were intercepted, including communications in which he discussed potential cabinet members before he was elected in July 2012, according to Greenwald.
Brazilian Foreign Minister Luiz Alberto Figueiredo said that, if proven, the report that Rousseff was spied on "represents an unacceptable and impermissible violation of Brazilian sovereignty".
Communications Minister Paulo Bernardo said the scope of the espionage was broader and more serious than had initially been thought and that US explanations had so far been "false."
US Director of National Intelligence James Clapper, responded to the allegations in a statement Sunday.
"The United States collects foreign intelligence -- just as many other governments do -- to enhance the security of our citizens and protect our interests and those of our allies around the world," he said.
It was "not a secret" that US intelligence agents collected economic and financial data, including information about financing terror, he stressed.
The practice helped provide the US and its allies with "early warning" of potential international financial crises, as well as about the economic policy or behavior of other countries that could affect global markets.
"Our collection of information regarding terrorist financing saves lives," he added.
"What we do not do, as we have said many times, is use our foreign intelligence capabilities to steal the trade secrets of foreign companies on behalf of -- or give intelligence we collect to -- US companies to enhance their international competitiveness or increase their bottom line."