Snowden's responses to questions by members of the European Parliament were released Friday, the New York Times reported. He said he approached more than 10 National Security Agency officials.
The NSA has previously said it found no sign that Snowden had tried to work internally. His leaks have resulted in his being charged under the Espionage Act and have embarrassed the U.S. government and many of its allies.
Snowden said he got warnings that complaints could get him into trouble or that they would have no effect.
"Even among the most senior individuals to whom I reported my concerns, no one at NSA could ever recall an instance where an official complaint had resulted in an unlawful program being ended, but there was a unanimous desire to avoid being associated with such a complaint in any form," he said.
Snowden also said he has not worked with Chinese or Russian intelligence agencies. He traveled to Russia, where he received temporary asylum, from Hong Kong.
Also Friday, the Foreign Intelligence Surveillance Court said the government has not provided a convincing reason to keep electronic data for more than five years, the Hill reported.