RIO DE JANEIRO (AP) — National Security Agency leaker Edward Snowden wrote in "an open letter to the Brazilian people" that he would be willing to help Brazil's government investigate U.S. spying on its soil, but that he could do so only if granted political asylum.

In a letter obtained and published early Tuesday by the respected Folha de S. Paulo newspaper, Snowden said he's been impressed by the Brazilian government's strong criticism of the massive NSA spy program targeting Internet and telecommunications around the globe, including monitoring the mobile phone of Brazilian President Dilma Rousseff.

Brazilian senators have asked for Snowden's help during hearings about the NSA program's aggressive targeting of Brazil, an important transit hub for trans-Atlantic fiber optic cables that are hacked.

"I've expressed my willingness to assist where it's appropriate and legal, but, unfortunately, the U.S. government has been working hard to limit my ability to do so," said the letter, translated into Portuguese by the newspaper. It didn't make the English original available online.

"Until a country grants me permanent political asylum, the U.S. government will continue to interfere with my ability to speak out," the letter added.

Early morning calls to Brazil's presidential office and to the Foreign Ministry rang unanswered.

Britain's Guardian newspaper first published accounts of the NSA's spy programs in June, based on some of the thousands of documents Snowden handed over to the Brazil-based American journalist Glenn Greenwald and his reporting partner Laura Poitras, a U.S. filmmaker.

Rousseff canceled an October visit to Washington that was to include a state dinner. She has joined Germany in pushing for the United Nations to adopt a symbolic resolution which seeks to extend personal privacy rights to all people.

Rousseff has also ordered her government to take several measures, including laying fiber optic lines directly to Europe and South American nations, in an effort to "divorce" Brazil from the U.S.-centric backbone of the Internet that experts say has facilitated NSA spying.

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The Snowden letter was published one day after a U.S. district judge ruled that the National Security Agency's bulk collection of millions of Americans' telephone records likely violates the U.S. Constitution's ban on unreasonable search. The case is likely to go all the way the Supreme Court for a final decision.

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