A test of a sea-based missile defence system was postponed for a day after a sailboat entered a hazard zone off Hawaii, a defence spokesman said.
A US warship was set to attempt to destroy the mock warhead of a medium-range missile over the Pacific with a new interceptor missile on Wednesday in the latest of a series of tests of the sea-based system.
But the test was scrubbed because a "sailboat transiting the hazard zone would not be able to clear the area before the launch window closed," said Rick Lehner, a spokesman for the US Missile Defence Agency.
The test comes amid tensions over North Korean preparations to launch a long-range missile, but Lehner said the missile defence test had been planned for months.
"It has nothing to do with North Korea or anything else," he said.
It was the second test intercept of a separating warhead, but the first with an operationally configured interceptor missile that is slated for deployment in the US Navy later this year.
The test involves a medium-range target missile that will be launched from a site in Kauai, Hawaii.
An Aegis-guided missile cruiser off Kauai will fire a ship-based SM-3 Block IA missile in an attempt to intercept the mock warhead after it separates from the main body of the target missile.