The Russian military's drive to revamp its Soviet-era missile arsenal has suffered a major setback after a nuclear-capable missile touted as the new pride of its rocket forces failed again in testing.

The submarine-launched Bulava intercontinental missile has now reportedly failed on more than half of its 11 test-firings and the latest launch was particularly disastrous as it blew up before completing the first stage.

The defence ministry late Thursday confirmed that the Bulava had exploded after launch from the nuclear-powered submarine Dmitry Donskoy off northern Russia "due to a failure in the first stage".

It was the sixth failure in 11 test launches, according to the specialist military newswire of the Interfax news agency. ITAR-TASS said the flight lasted a mere 28 seconds.

"It is a big setback that puts into doubt the validity of the nuclear deterrent," independent Russian military analyst Pavel Felgenhauer told AFP. "This time it was in the first stage. That's not good."

"Of course, nuclear weapons serve as deterrents. If they don't work, but you can pretend they do, then they can still do the job. But here (with the Bulava) we don't even have a pretence," he added.

A source in the goverment's defence industry commission admitted to Interfax that it was "bad" that the problem occurred in the first stage as "we thought this had been fully worked out."

The source indicated there was no prospect of scrapping the project. "I think the situation with the missile is not hopeless. No test of a new missile goes ahead without such problems."

The Bulava, which can be equipped with up to 10 individually targeted nuclear warheads, has a maximum range of 8,000 kilometres (5,000 miles).

It is the sea-based version of the Topol-M, Russia's new surface-to-surface intercontinental missile, and designed to be launched from Moscow's newest Borei class of submarines.

The last test on December 23 also ended in failure when the missile exploded in mid-air after launch.

The Bulava is the standard-bearing project for the Russian military which is seeking to replace old Soviet-era warhorse missiles with more modern models as part of a major military reform.

In a sign of the importance of the project, the Kommersant newspaper said a colossal 40 percent of the defence ministry's purchasing budget is currently being spent on development of the Bulava.

"The failure exposes the serious problem Russia has in replacing Soviet-made strategic delivery systems. It puts Russia into a position where its nuclear superpower status is in question," said Felgenhauer.

The overall commander of Russia's missile forces, General Nikolai Solovtsov, has called for the nuclear arsenal to be completely revamped by 2020.

Defence expert Joseph Henrotin said there was a "fundamental problem in conception" to the idea of adapting a surface-to-surface missile like the Topol-M to a sea-to-surface version like the Bulava.

The technical problems were being compounded by the retirement of many Russian engineers and the drying-up of funding since the end of the Cold War, said Henrotin.

The problems with Bulava also come amid delicate negotiations between Russia and the United States aiming to renew by the end of the year the 1991 Strategic Arms Reduction Treaty (START) on reducing nuclear arms.

"The Russians' credibility is threatened by these difficulties. The United States will see a country that has problems putting itself into order," said Henrotin, editor of the French monthly Defence and International Security.

Meanwhile, the RIA Novosti news agency cited a Russian intelligence source as saying that "sabotage" in the production chain had not been ruled out.

The source said the problems could have arisen through poor quality control but "the defect could have come into the production chain as a result of criminal negligence, which also could be seen as sabotage."