US intelligence leaker Edward Snowden offered to help Brazil defeat US spying Tuesday but, in an open letter, said he needs permanent political asylum to do so.

The move was widely interpreted as a request for asylum in Brazil, including by the Folha de Sao Paulo newspaper that published the letter in both English and Portuguese.

Snowden, by downloading a vast trove of classified documents while working as an intelligence contractor for the NSA, has revealed a vast NSA program that culls information from telephone calls and emails around the world, including in Brazil.

In the letter, he writes that US officials justify the actions by saying they aim "to keep you safe."

But, he says, "these programs were never about terrorism: they're about economic spying, social control, and diplomatic manipulation. They're about power."

"Now, the whole world is listening back, and speaking out, too," he said.

"The culture of indiscriminate worldwide surveillance, exposed to public debates and real investigations on every continent, is collapsing."

Snowden does not request asylum from Brazil in the letter, but notes Brazilian senators "have asked for my assistance with their investigations of suspected crimes against Brazilian citizens."

Snowden says he is willing to help "wherever appropriate and lawful" but adds that "unfortunately the United States government has worked very hard to limit my ability to do so."

"Until a country grants permanent political asylum, the US government will continue to interfere with my ability to speak," he says.

Folha, which published the letter, interpreted it as confirming that Snowden's goal is to come to Brazil.

Glenn Greenwald, who has written about many of the documents released by Snowden, is based in Brazil. The Latin American country has a long tradition of granting asylum.

Greenwald's partner, Brazilian journalist David Miranda, began a campaign last month in support of an asylum request there.

"Brazil is one of the rare countries with the strength to give him asylum," Miranda told AFP Tuesday.

He said Snowden had written the letter in response to questions over why he was not cooperating with the Brazil probe.

"It's clear that he can't do it while he doesn't have permanent asylum," Miranda said.

But the Brazilian foreign ministry told AFP Tuesday it had not "received any official request" for asylum from Snowden.

In July, the former intelligence contractor had informally requested asylum from a number of countries, including Brazil, before Russia granted him a year-long visa.

In the letter to Brazilians, Snowden praises Brazil's fierce reaction to news it was among those the NSA spied on.

President Dilma Rousseff canceled a visit to Washington in October after learning of it and helped sponsor a UN resolution aimed at protecting "online" human rights.

Rousseff's cell phone was monitored by the US surveillance program, as were the state oil company Petrobras and everyday Brazilian citizens.

Snowden's apparent bid for Brazil asylum is being supported by Amnesty International's Brazilian office and rights group Avaaz.

"Edward Snowden has every right to seek permanent asylum and the Brazilian authorities should respond to his initial asylum claim seriously," said Atila Roque, Brazil Director of Amnesty International.

"It is his right to seek international protection, and it's also Brazil's international obligation to review and decide on his request under the refugee convention."

"The Brazilian people, who suffered political persecution and mass surveillance during the years of dictatorship in the country, know all too well its abusive effects," said Roque.

Avaaz director Michael Mohallem said: "Snowden is now trapped alone in Russia on a short term visa. Brazil could offer him the hero's welcome he deserves.”

[Image via Agence France-Presse]