The American Civil Liberties Union is suing the federal government, seeking to force a response to its request for documents about drone missile strikes against terror suspects.

The complaint, filed in New York's southern district, says the Justice and Defense Departments and the CIA have failed to respond to the ACLU's year-old request for records relating to drone strikes under the Freedom of Information Act. While many details of the strikes are classified, President Barack Obama has acknowledged that the U.S. engages in the practice.

The lawsuit says the government failed to make a reasonable effort to search for records responsive to the request.

The ACLU says Obama in May 2013 promised greater transparency about drone strikes, but has failed to deliver.

The government had no immediate comment.