File image of Titan 4 rocket at Complex 40. Photo: Lockheed Martin TV/Spaceflight Now

Launch of the Titan 4 rocket from Cape Canaveral on June 3 has been postponed due to a problem with its secret spy satellite payload, Air Force officials have confirmed.

"The National Reconnaissance Office requested a slip in the launch of the Titan/Centaur. The request was made on Monday," the Air Force's Launch Program Office at the Space and Missile Systems Center said in a written statement.

The NRO is the classified government agency responsible for building and operating the country's fleet of reconnaissance satellites.

An agency spokesman said details on the spacecraft's problem would not be released.

A new launch date has not been set, but the delay is more than a matter of a few days, according to the spokesman.

When the Lockheed Martin-built rocket does fly, it will use a liquid-fueled Centaur upper stage to propel the payload into orbit from the Cape's Complex 40.

The delay frees up the Air Force-controlled Eastern Range -- the vast network of tracking, communications and safety systems -- that is used by all Cape launches.

Space shuttle Endeavour is slated for launch on May 30 to exchange the resident crews living aboard the International Space Station. When the Titan 4 was scheduled for a June 3 liftoff, the shuttle would have gotten only two launch attempts on the Range before waiting until after the Titan had its shot. Now, the shuttle should get more launch opportunities in case weather or technical problems are encountered.