The Navy is refusing to detail its sonar use for a federal court in a case involving potential harm to whales, saying the information could jeopardize national security.

Complying with a federal judge's order to hand over the information would require disclosure of sensitive and classified material, the Navy said in a news release Tuesday.

The Natural Resources Defense Council is suing the Navy to ensure sailors use sonar in a way that doesn't harm whales and other marine mammals.

Critics say active sonar, which sailors use by pumping sound through water and listening for objects the sound bounces off of, can strand and even kill marine mammals. A U.S. Congressional Research Service report last year found Navy sonar exercises had been responsible for at least six mass deaths and unusual behavior among whales. Many of the beached or dead animals had damaged hearing organs.

The Navy acknowledges sonar may harm marine mammals but says it already takes steps to protect whales, such as posting lookouts.

In considering the lawsuit, U.S. District Judge Florence-Marie Cooper issued an order for the Navy to submit data for the case on when and where sailors have used sonar since 2003. Cooper instructed the Navy to list the latitude and longitude of where it used mid-frequency active sonar, how long it used the sonar, and the times and dates.

The Navy said in its new release that it refused to comply citing state secrets privilege, which allows government officials to keep information secret on national security grounds.

"If you look at it in the aggregate, it paints a picture that we wouldn't want to paint for our adversaries," said a Navy official who spoke on condition of anonymity because the matter was still being litigated.

Joel Reynolds, a Natural Resources Defense Council attorney, said he would challenge the Navy's position. The council and the court needs the data to ascertain how the Navy has complied with environmental laws when sailors use sonar.

"This latest invocation of state secret privilege is one more attempt to deprive the public of the information it needs to determine whether the Navy is illegally and needlessly endangering the marine environment," Reynolds said.