US officials blamed a radar malfunction for the failed test

A US missile defence test designed to shoot down long-range missiles was aborted when the radar system failed.

Rick Lehner, a Missile Defense Agency spokesman, said the target missile represented the type of technology that North Korea or Iran might develop.

The target was launched from the Marshall Islands in the Pacific and the interceptor missile from California.

The Pentagon said those two components performed as expected, but the sea-based X-band radar system failed.

The system has been under development for many years at the cost of tens of billions of dollars, and the Pentagon will be embarrassed by the failure, says the BBC security correspondent Nick Childs.

In the exercise on Sunday, a target missile was fired from Kwajalein in the Marshall Islands, and the interceptor from Vandenberg Air Force base in California, the Missile Defense Agency said.

The target represented "the type of technology that a country such as North Korea or Iran might be able to develop in the future that would threaten the United States," Mr Lehner told the French news agency, AFP.

The test came as the Pentagon released a report warning that Iran and North Korea's intermediate and shorter-range missiles posed regional threats to US forces and their allies.

Last week, the US said it was speeding up the deployment of ships off the Iranian coast and Patriot anti-missile systems in several Gulf countries to counter what it sees as a growing Iranian threat.

An investigation would be conducted into the cause of the test failure, US officials said.