WASHINGTON, Jan. 8 (Xinhua) -- A highly classified U.S. spy satellite that was launched aboard a SpaceX rocket on Sunday failed to reach orbit and might have been lost, U.S. media reported Monday, citing officials briefed on the mission.

"We do not comment on missions of this nature; but as of right now reviews of the data indicate Falcon 9 performed nominally," a SpaceX spokesperson said in a statement.

The mysterious Zuma satellite, built by American aerospace and defense technology company Northrop Grumman, failed to separate from the second stage of the Falcon 9 rocket and is assumed to have broken up or plunged into the sea, according to new website Time, who quoted two anonymous U.S. officials as saying.

The satellite is assumed to be "a write-off," the report said, adding that an investigation is under way, but there is no initial indication of sabotage or other interference.

Zuma was launched on a Falcon 9 rocket from the Cape Canaveral Air Force Station in Florida on Sunday evening.

Very little is known about the nature of the mission, as no U.S. government agency has claimed responsibility for it.

Previously, SpaceX has launched two classified payloads for the U.S. government during the past year.

Launched in May, the NROL-76 spy satellite was for the National Reconnaissance Office. The other was a non-crewed X-37B space plane for the U.S. Air Force, which lifted off in September.