The US military says it failed to shoot down a ballistic missile in a test resembling an Iranian or North Korean strike after a radar malfunctioned.
The test was carried out on Sunday at a US Army site at the Kwajalein Atoll in the Marshall Islands but the target missile was not intercepted as planned.
A spokesman for the Missile Defence Agency, Rick Lehner, says an investigation into the test has been opened and it will take several weeks before they have an initial report.
Sunday's test follows reports that the US military is speeding up deployment of defences against potential Iranian missile attacks in the Gulf to heed off any possible retaliation.
