The United States Defence Department is to conduct an extensive review after a test of its missile defence system failed.

A prototype missile interceptor, aimed at a mock incoming nuclear missile, failed to make impact.

A spokesman at the Pentagon said a preliminary report would not be available before Thursday, and the reason for the failure may not be known for several weeks.

President Clinton is due to decide later this year whether to go ahead with the missile defence system, which would cost more than twelve-billion dollars.

Of five previous tests, only the most recent, last October, succeeded. Russia and China strongly oppose Washington's plans, saying it will spark another arms race.

But a BBC correspondent in California says it is North Korea which the Clinton administration believes poses the most immediate threat of long-range attack to the United States.

From the newsroom of the BBC World Service