The Pentagon has said an aircraft, not a missile, was the probable cause of a condensation trail off the coast of California on Monday.
A CBS News helicopter captured what looked like a missile's vapour trail about 35 miles (56km) offshore.
The Pentagon made its announcement after examining video of the plume and its missile launch detection systems.
"There is no evidence to suggest it was anything other than an aeroplane," said Pentagon spokesman Col David Lapan.
The vapour trail, which some said appeared to be coming from a missile moving vertically into the sky, was filmed by the news helicopter near Los Angeles, in southern California.
The footage sparked wide media interest on Tuesday after the Pentagon said it was unable to explain the source of the vapour.
Some physicists said earlier on Tuesday they believed the trail had been left by an aircraft, and that on a clear day vapour can appear to rise vertically as the result of an optical illusion.
Under normal circumstances, the launch of a US missile would require several different authorisations and notifications.
Pentagon officials canvassed the US government, examined Federal Aviation Administration radar tracks and analysed their own missile launch detection systems before saying they were satisfied with the explanation that the plume was created by an aircraft.
Several planes but no rockets were detected by radar systems on Monday, Col Lapan said.