The test record of the missile defence system is mixed

The Missile Defence Agency (MDA) said a dummy long-range missile launched from Alaska was hit by an interceptor sent up from California.

The missile defence system under development uses radar and satellites to detect enemy missile launches and to guide interceptors to their targets.

But it has a mixed record, with only five successful tests out of nine.

During the last attempts to launch interceptor missiles in December 2004 and February 2005, the interceptors failed to launch from their silos.

Friday's test was the first time the Vandenberg base in central California has been used to launch the ground-based interceptor.

It was also the first since North Korea test-fired ballistic missiles in July.

Missile shield

The MDA said the $85m test was an important exercise aimed at protecting the United States against a limited long-range ballistic missile attack.

The US test was designed to determine whether the system could distinguish the target warhead from its launcher or a decoy.

MDA spokesman Rick Lehner said the agency had been hoping for a "close approach", with the interceptor manoeuvring itself near to the warhead.

The actual intercept was "a bonus", he said.

He said it would take weeks to review the data collected during the test.

The results, he said, would help improve the performance of the planned shield against the type of missile that could be used to attack a US city with a weapon of mass destruction.

The shield also includes components based at sea and in space.

But critics say the missile defence system is a waste of money. The Associated Press reports that more than $100 billion (�52 billion) has been spent on America's missile-defense system since 1983.