An attempt to launch an interceptor missile as part of the U.S. missile defence shield failed early Wednesday in the first test of the system in nearly two years.

The Missile Defense Agency said the ground-based interceptor automatically shutdown "due to an unknown anomaly" shortly before it was to be launched from Kwajalein Atoll in the central Pacific Ocean.

A target missile carrying a mock warhead successfully launched from Kodiak, Alaska, at 12:45 a.m. ET.

Officials said they would now review the pre-launch data to determine the cause of the shutdown.

The missile defence shield was meant to be in operation by the end of 2004.

In earlier tests, missile interceptors had a record of five-for-eight in hitting target missiles.

Wednesday's test had been put off several times because of bad weather, and a malfunction of a recovery vessel not directly related to the equipment being tested, The Associated Press reported.

U.S. President George Bush announced the system in 2002, saying it would help protect against a missile attack from rogue states such as North Korea and other parts of eastern Asia.

Last August, Ottawa agreed to amend its agreement in NORAD to allow the U.S to use the missile warning system for its controversial plan for a ballistic missile defence system.

However, it seems that Bush is seeking more help from Canada. On his recent visit to Halifax, Bush publicly asked for Ottawa's participation in the system.

Prime Minister Paul Martin has said he is against the "weaponization of space" -- a claim he reiterated in his year-end interview with CTV News anchor Lloyd Robertson and Ottawa bureau chief Craig Oliver.