US plans for a multi-billion dollar anti-missile defence shield have suffered a further setback after the failure of a second test in two months.
Testing of the missile system has had mixed success
An interceptor missile failed to lift off from its silo during the test on the Pacific Ocean's Marshall Islands.
The US Missile Defense Agency said the malfunction of ground support equipment rather than defects in the missile itself were most likely to blame.
Similar problems hit a test in December, the first for two years.
Monday's test was carried out at the Ronald Reagan site on Kwajalein Island.
The interceptor missile was meant to shoot down a target missile that launched from Kodiak Island in Alaska.
"The reason for not launching is under investigation, and program officials are reviewing data to determine the cause," the Missile Defense Agency said in a statement.
Spokesman Rick Lehner was quoted by the Associated Press as saying early indications suggested a malfunction with the ground support equipment.
'Son of Star Wars'
A previous test in December - the first to be carried out in almost two years - suffered similar problems.
The interceptor missile failed to take off and was automatically shut down on its launch pad, the Pentagon said at the time.
Faulty software is thought to have been to blame.
In earlier tests, target missiles have been successfully intercepted in five out of eight attempts.
The US is spending $10bn a year on what would be a defensive screen for the whole of the US, with the ability to track and destroy incoming ballistic missiles.
The goal, announced by US President George W Bush in 2002, was to have a basic ground-based shield in place by the end of last year.
The programme has been nicknamed "son of Star Wars" after the original Strategic Defence Initiative - or "Star Wars" - outlined by President Reagan in the 1980s.