THE United States' controversial National Missile Defence system appeared in serious doubt yesterday after a rocket failed to destroy a target warhead high above the Pacific. Pentagon officials expressed frustration and dismay after a relatively routine technical hitch scuppered the US$100 million (HK$778 million) operation before its most crucial phase. The failure is likely to buoy critics of the project, especially Beijing and Moscow. As a Minuteman missile soared into space from Vandenberg air force base in California, the so-called 'kill vehicle' never detached from its booster rocket after lifting off from the Marshall Islands. Officials and defence contractors had been hoping successful 'updates' from powerful prototype land-based radars would send the high-speed vehicle crashing into the missile to prove its viability ahead of a crucial recommendation to the White House. The test had failed before those signals came into play. Large screens set up at the Pentagon and the Boeing aerospace headquarters in Seattle to film a massive explosion more than 200km above Hawaii registered only blank space. It was the second failure in three tests and the first to definitely trial the 'update' signals. A grim-faced US air force Lieutenant-General Ronald Kadish, director of the missile defence effort, said: 'We did not intercept the warhead tonight. We are disappointed.' He said the kill-vehicle's failure to detach 'was not even on my list' of possible hitches. Early indications suggested the vehicle never received an internal signal from the booster to de-link. General Kadish said it was too early to draw conclusions and the impact on any recommendation from his boss, Defence Secretary William Cohen. Other new elements of the system - an early-warning satellite and the X-band radar - had functioned perfectly. He said that ironically, the booster involved far older technology from the Minuteman missile system, chosen for the tests for its 'reliability'. Mr Cohen is due to make a decision based on technical viability and cost so President Bill Clinton can give the final green light in autumn, after taking into account various threats and damage to international arms control efforts. China, Europe and Russia have warned the system - geared only to thwarting isolated attacks from 'rogue' nations such as Iran and North Korea rather than a full-scale nuclear offensive - will spark an arms race. Russian President Vladimir Putin has repeatedly warned the system, with its use of space and special radar, breaks the 1972 Anti-Ballistic Missile Treaty. Russian officials said yesterday the failure showed that America's planned creation of an anti-missile shield was illogical and technically impossible. The British Government declined to comment, saying it was 'a matter for the Americans'. Ranks of leading US scientists and former government officials also object, saying the US$60 billion project will do little to protect the US while creating new instabilities across the world. The project is being driven by intelligence estimates that show North Korea could have the ability to strike US cities by 2005. A top-level meeting is scheduled for Tuesday to review threats posed by an estimated two dozen states with active missile programmes.