The missile was destroyed less than 30 minutes after launch

It was the first test of the "hit-to-kill" system since George W Bush took office, and the first of a total of four tests reported to have been wholly successful.

But Russia condemned the test on Sunday, saying the exercises could jeopardize all previous agreements on nuclear disarmament.

Environmentalists also denounced the tests, saying they threatened to re-start a global nuclear arms race.

'Mission success'

Staff monitoring the test at the Pentagon saw an enormous white flash on their video screens when the missiles collided.

We believe we have a successful test in all aspects... the kill intercept was confirmed by all of our sensors

Lt General Ronald Kadish

The interceptor was fired 21 minutes after the Minuteman missile was launched.

It managed to disregard the decoy that the Minuteman was carrying and smash into its intended target, the dummy warhead, at 0309GMT.

"We believe we have a successful test in all aspects... the kill intercept was confirmed by all of our sensors," said Lt General Ronald Kadish, speaking at the Pentagon.

But in a word of caution he warned that it would take around two months to fully analyse the results of the test.

Of the past three tests, two were total misses, and even the partially successful test had technical problems.

The only apparent problem was a short delay in starting, for which protestors from the environmental organisation Greenpeace claimed responsibility.

Eighteen of its activists were arrested for attempting to disrupt the launch.

Opposition

The Minuteman II missile left a vapour trail across the sky

A Russian statement said the test threatened the international structure of nuclear disarmament.

"A logical question again arises - why take matters to the point of placing under threat the entire internationally agreed structure of nuclear disarmament and non-proliferation, including its core, the 1972 ABM treaty?" Ministry spokesman Alexander Yakovenko said in a statement.

BBC Moscow correspondent Stephen Dalziel says the Chinese and Russian leaders may well agree a joint statement on their objections to the project after President Jiang Zemin arrives in Moscow on Sunday for a four-day official visit.

Both countries are sceptical about the threat posed by countries like North Korea and Iraq, he says, and hawks in both countries suggest that the system could be employed as part of an attack on them.

Democrat pressure

There are also pressures at home, with key Democrats insisting that the pace of research must be more deliberate and the test programme more rigorous.

Many see no reason or need to violate the ABM treaty in the immediate future.

But the Bush team seems intent on placing missile defence on a fast track, our Washington correspondent says.

In September, testing will begin on a ship-based system.

Eventually trials will also begin on a massive laser mounted on a jumbo jet.