WASHINGTON — Edward J. Snowden, the former National Security Agency contractor who leaked a trove of documents revealing the agency’s surveillance operations, said he raised his concerns to more than 10 officials, “none of whom took any action to address them,” before he decided to give the documents to journalists.

Mr. Snowden’s comments, in written answers to questions by members of the European Parliament that were released on Friday, amplified previous assertions that he initially tried to raise concerns internally about surveillance collection he believed went too far.

An N.S.A. spokeswoman declined to comment, but the agency has previously said its internal investigation, including interviews with co-workers, found no evidence that he had brought concerns to the attention of anyone.

But in his written testimony, Mr. Snowden insisted that he had, adding that his efforts had elicited two types of responses. Some people, he said, responded with “well-meaning but hushed warnings not to ‘rock the boat’ ” for fear of retaliation like being investigated by the F.B.I. as a suspected leaker.