Former National Security Agency (NSA) contractor Edward Snowden has written "an open letter to the people of Brazil," offering to help the Brazilian government investigate US spying, and making a veiled plea for permanent political asylum. The letter was published in Portuguese Tuesday in Folha de S. Paulo, a Brazilian newspaper. David Miranda, the partner of outspoken Rio-based journalist Glenn Greenwald, later published an English-language version of the letter to his Facebook page.

In the letter, Snowden praised Brazilian leaders for speaking out against American spying after it was revealed that the NSA had conducted widespread surveillance of companies and civilians in Brazil, including President Dilma Rousseff. The revelations have raised diplomatic tensions in Brazil, prompting Rousseff to call for the country to build a new fiber-optic system to evade NSA monitoring.

Snowden, who is currently living as a fugitive in Russia, leaked classified documents on the NSA's spy programs earlier this year to Greenwald, who reported on them in June for the Guardian. In the letter published Tuesday, he said that Brazilian lawmakers have asked him for assistance in investigating the NSA's operations in Brazil and that he is willing to do so, though his efforts have been hampered without political asylum.

"I have expressed my willingness to assist wherever appropriate and lawful."

"I have expressed my willingness to assist wherever appropriate and lawful, but unfortunately the United States government has worked very hard to limit my ability to do so," the letter reads. "Until a country grants permanent political asylum, the US government will continue to interfere with my ability to speak."

In October, Greenwald urged Brazilian senators to grant asylum to Snowden, claiming that the leaker could help the government better understand the NSA's programs. Snowden had previously requested asylum from Brazil and other countries, before being granted temporary asylum by Russia in August.

A senior NSA official this week suggested that the US may be considering offering amnesty to Snowden, saying the idea is "worth having a conversation about" in an interview with 60 Minutes, though White House Press Secretary Jay Carney sought to curtail that speculation on Monday, telling reporters that the contractor should return to the US and face criminal charges.

"Mr Snowden has been accused of leaking classified information and he faces felony charges in the US," Carney said. "He should be returned to the United States as soon as possible, where he will be accorded full due process."