By Paulo Prada and Asher Levine

RIO DE JANEIRO/SAO PAULO (Reuters) - The U.S. government tapped into computer networks of companies including Google Inc. and Brazilian state-run oil firm Petroleo Brasileiro SA, according to leaked U.S. documents aired by Globo, Brazil's biggest television network.

A week after it broadcast a report that the U.S. National Security Agency spied on the presidents of Brazil and Mexico, Globo said the agency had also spied on major companies.

It showed slides from an NSA presentation, dated May 2012, that it said was used to show new agents how to spy on private computer networks.

In addition to Google and Petrobras the presentation suggested the NSA had tapped into systems operated by France's foreign ministry and the Society for Worldwide Interbank Financial Telecommunication, an international bank cooperative known as Swift, through which many international financial transactions take place.

The report did not say when the alleged spying took place, what data might have been gathered or what exactly the agency may have been seeking.

As with its previous report, Globo disclosed the information in coordination with Glenn Greenwald, an American blogger and journalist for the Guardian newspaper, who has worked with former NSA analyst Edward Snowden to expose the extent of U.S. spying at home and abroad.

During an interview in the Globo broadcast, Greenwald said the documents he obtained from Snowden contain "much more information on spying on innocents, against people who have nothing to do with terrorism, or on industrial issues, which need to be made public."

In an email exchange with Reuters, Greenwald declined to discuss the report further.

Petrobras, which has made some of the world's biggest oil finds in recent years, did not respond to requests for comment on Sunday. Spokespeople for Swift and Google couldn't be reached for comment. Officials at the French embassy in Brazil also could not be reached.

Story continues

TRADE SECRETS

James Clapper, the U.S. Director of National Intelligence, said U.S. agencies do collect information about economic and financial matters and that it is used to combat terrorist financing and predict problems that could lead to financial crises or disrupt financial markets.

"What we do not do," Clapper said in a statement, "is use our foreign intelligence capabilities to steal the trade secrets of foreign companies on behalf of - or give intelligence we collect to - U.S. companies to enhance their international competitiveness or increase their bottom line."

Especially before the Snowden revelations began three months ago, U.S. officials regularly accused China of stealing trade secrets from Western countries, including oil and gas firms.

At the very least, revelations of U.S. spying on Petrobras are likely to further complicate the tension between the United States and Brazil over allegations that the NSA spied on the private phone calls and emails of Brazilian President Dilma Rousseff.

Brazil has demanded a formal apology and Rousseff aides have said the issue could derail a state visit she is due to make to the United States in October.

The tensions led to an impromptu meeting between Rousseff and U.S. President Barack Obama last week at the G20 meeting in Russia. Obama said he would investigate the allegations.

Any spying on Petrobras is sure to raise hackles in Brazil, which has long been suspicious of foreign designs on its abundant natural resources.

U.S. officials, including Obama on a 2011 trip to Brazil and Vice President Joe Biden during a visit in June, have cited the importance of Brazil's big new oil finds and flagged intentions to work closely with the country for future energy needs.

Brazil's so-called sub-salt polygon, where many of the new finds have been discovered, may contain as much as 100 billion barrels of oil, according to Rio de Janeiro State University. One find alone, the giant Libra field, has estimated reserves of up to 12 billion barrels of oil, or enough to supply all U.S. oil needs for nearly two years.

(Additional reporting by Joseph Menn in San Francisco; Editing by Kieran Murray and Christopher Wilson)