Updated

A civil rights group sued the New York Police Department on Monday seeking to learn more about a plan to use license plate readers and a network of 3,000 surveillance cameras to help protect lower Manhattan from terrorist threats.

The New York Civil Liberties Union claims the NYPD has moved forward with its plan without explaining how the department will use and store images and data captured by the video cameras, license-plate readers and other security devices.

"A plan of this scope, expense and intrusiveness demands robust public debate and legislative oversight," said Donna Lieberman, the group's executive director. "The public has a right to this information."

The department already has turned over 91 pages of material about the so-called Lower Manhattan Security Initiative, which is expected to cost tens of millions of dollars. But the NYCLU said the documents were redacted, and that more information should be disclosed.

The NYPD "must have hundreds if not thousands of documents that would be responsive to the NYCLU's request," says the suit, filed in state court.

Police spokesman Paul Browne said the department has provided everything it could, "short of a road map terrorists could use for another attack."

The security plan, prepared by the NYPD's counterterrorism division, would rely on 116 stationary and mobile license-plate readers and a network of 3,000 closed-circuit cameras -- both public and private -- that would be monitored by officers at a command center. It was modeled in part after the "ring of steel" surveillance measures in London's financial district.

Police officials say photos and license plate numbers would be cross-checked with information about potential terror suspects and suspicious vehicles. They insist data deemed innocent would be purged from police records after 30 days.