WASHINGTON (REUTERS) - United States (US) intelligence officials released new documents on Wednesday showing that the National Security Agency (NSA) may have unintentionally collected as many as 56,000 emailed communications of Americans between 2008 and 2011.

The officials revealed the documents as part of an effort to explain how the NSA spotted, and then fixed, technical problems which led to the inadvertent collection of emails of American citizens without warrants.

The move is the Obama administration's latest response to continuing controversy over alleged electronic eavesdropping excesses by the NSA.

The documents included a formerly "top-secret," but newly-declassified ruling by the ultra-secretive Foreign Intelligence Surveillance Court in which the court itself, in an obscure footnote, estimates, based on data supplied by NSA, that between 2008 and 2011, the agency might have unintentionally collected as many as 56,000 emailed communications of Americans.

US intelligence officials who agreed to answer questions about the documents' contents told reporters the domestic emails were collected in the execution of a program designed to target the emails of foreign terrorism suspects.

According to the officials and a court document which the administration released, the NSA decided to "purge" the material after discovering it was inadvertently collected.

Details about the secretive surveillance programs have been brought to light in recent months by fugitive US intelligence contractor Edward Snowden, who leaked classified documents to media outlets.