The federal government has repeatedly violated legal limits governing the surveillance of U.S. citizens, according to previously secret internal documents obtained through a court battle by the American Civil Liberties Union.

In releasing 900 pages of documents, U.S. government agencies refused to say how many Americans' telephone, e-mail or other communications have been intercepted under the Foreign Intelligence Surveillance Act - or FISA - Amendments Act of 2008, or to discuss any specific abuses, the ACLU said. Most of the documents were heavily redacted.

However, semiannual internal oversight reports by the offices of the attorney general and director of national intelligence identify ongoing breaches of legal requirements that limit when Americans are targeted and minimize the amount of data collected.

The documents note that although oversight teams did not find evidence of "intentional or willful attempts to violate or circumvent the law . . . certain types of compliance incidents continue to occur," as a March 2009 report stated.

The unredacted portions of the reports refer only elliptically to what those actions were, but the March 2009 report stated that "information collected as a result of these incidents has been or is being purged from data repositories."

All three reports released so far note that the number of violations "remains small, particularly when compared with the total amount of activity." However, as some variously put it, "each [incident] - individually or collectively - may be indicative of patterns, trends, or underlying causes, that might have broader implications." and underscore "the need for continued focus on measures to address underlying causes." The most recent report was issued in May.

In a statement Thursday, the ACLU said that violations of the FISA Amendments Act's "targeting and minimization procedures . . . likely means that citizens and residents' communications were either being improperly collected or 'targeted' or improperly retained and disseminated." The ACLU has posted the documents on its Web site.

A spokesmen for Director of National Intelligence James Clapper did not immediately comment on the ACLU statement.

In an e-mailed statement late Thursday, a spokesman for Attorney General Eric H. Holder Jr., Dean Boyd, said the new law "put in place unprecedented oversight measures, reporting requirements and safeguards to protect privacy and civil liberties," and that the reports cited by the ACLU were the product of "rigorous oversight" by the Justice Department and intelligence community. "In short, foreign intelligence surveillance is today carefully regulated by a combination of legislative, judicial, and executive-branch checks and balances designed to ensure strong and scrupulous protection of both national security and civil liberties," Boyd's e-mail said.

Melissa Goodman, staff attorney with the ACLU National Security Project, said, "It is imperative that there be more public disclosure about the FAA [FISA Amendments Act] violations described in these documents . . . as Congress begins to debate whether the FAA should expire or be amended in advance of its 2012 sunset."

Congress passed FISA in 1978 to prevent Americans' communications from being tapped without a warrant. Lawmakers amended the law in 2008 to broaden and clarify legal authorities after the Sept. 11, 2001, terrorist attacks and advances in Internet communications prompted fresh concerns over expanded surveillance powers.

The ACLU, human rights activists and other parties sued, charging that the new law violates the Fourth Amendment's prohibition of unreasonable searches. A U.S. district judge tossed out the case, which remains on appeal, and the ACLU has pursued a related Freedom of Information Act request.