The US government spied on Brazilian state-run oil giant Petrobras, according to intelligence documents released by Globo television.

Globo also said NSA spied on the private computer networks of Google and a company that facilitates most of the world's international bank transfers. But the report gave no information about what the agency might have obtained from Petrobras, Google and the Belgium-based Society for Worldwide Interbank Financial Telecommunication, an organisation better known as Swift.

It said the information was based on documents dated June last year.

Globo said it obtained the information from Glenn Greenwald, a columnist for The Guardian who obtained secret files from US National Security Agency leaker Edward Snowden.

A week ago, the network reported that the NSA had intercepted communication from the presidents of Brazil and Mexico.

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.

US President Barack Obama has vowed to ease tensions with Brazilian President Dilma Rousseff and Mexican President Enrique Pena Nieto, telling them he understood their reaction.

Rousseff, who is scheduled to visit Washington on October 23, has warned she will cancel the trip if she does not receive convincing explanations.