Brazilian President Dilma Rousseff has criticised the US over allegations it carried out electronic espionage.
Speaking at the opening of the UN General Assembly, Ms Rousseff said Brazil would adopt legislation and technology to protect itself from illegal intercepts.
She called Washington’s explanation that spying on Brazil was to protect nations from terrorists “untenable”.
Earlier this month, she cancelled a planned visit to Washington.
Ms Rousseff told the assembled leaders that Brazil had been a target of intrusions and intercepts carried out by a “global network of electronic espionage”.
She said that “corporate information – often of high economic and even strategic value – was at the centre of espionage activities”.
President Rousseff said such tampering with another country’s affairs was an “affront to the principles that must guide the relations among friendly nations”.
Her speech came a week after she called off a high-profile visit to the United States after a string of allegations about the extent of the US spying programme emerged.
Ms Rousseff rejected arguments put forward by the US that the illegal interception of information was aimed at protecting nations against terrorism.
“Brazil, Mr President, knows how to protect itself,” she said.
“We face, Mr President, a situation of a grave violation of human rights and civil liberties; of invasion and capture of confidential information concerning corporate activities, and especially of disrespect to national sovereignty,” she added.
The allegations of widespread espionage against Brazilian citizens were first published in July by Rio de Janeiro-based journalist Glenn Greenwald, a reporter for the British Guardian newspaper.
Mr Greenwald alleged that the NSA accessed all internet content that Ms Rousseff had visited online.
Earlier this month, another report by Mr Greenwald alleged that the NSA had also illegally accessed data from Brazil’s state oil company, Petrobras.
The company is due next month to carry out an important auction for exploration rights of an oil field off the Rio de Janeiro state coast.
Ms Rousseff said that her government would “do everything within its reach to defend the human rights of all Brazilians and to protect the fruits borne from the ingenuity of our workers and our companies”.
She asked the United Nations to play a leading role in regulating electronic technology and said Brazil would present proposals for a “civilian multilateral framework” for the governance and use of the internet and to protect web-based data.