The US Defence Department said yesterday it was trying to determine if a missile was launched on Monday off the coast of southern California and, if so, who might have fired it.
Spokesmen for the Navy and Air Force said they were looking into a video posted on the CBS News website that shows an object shooting across the sky and leaving a large contrail, or vapour trail, over the Pacific Ocean. The video was shot by a helicopter owned by the television station KCBS.
"Nobody within the Department of Defence has been able to explain what this contrail is, where it came from," the Pentagon spokesman Colonel Dave Lapan said.
Col Lapan said that "all indications" are that the Department of Defence was not involved with the mystery object, and that the contrail might have been created by something flown by a private company.
Normally any missile test would require notification so that mariners and pilots could be warned or air space closed. "It does seem implausible, and that's why at this point the operative term is 'unexplained'," Col Lapan said.
Missile tests are common off southern California. Launches are conducted from vessels and platforms on an ocean range west of Point Mugu.