Investigators have established that the latest test failure of the troubled Bulava ballistic missile was caused by a design flaw, rather than a faulty component, a Russian defense industry source said Tuesday.

"An investigation commission established in December that a design flaw in the device which controls the separation of the third stage had caused the latest failure of the Bulava missile," the source said.

It is the first time the Russian industry officials admit that there are problems with the original design of the submarine-launched ballistic missile (SLBM), which Russia hopes will be a key element of its nuclear forces.

The latest launch of the missile from the Dmitry Donskoy nuclear submarine in the White Sea ended in failure in early December 2009. Only five of 12 Bulava launches have been officially reported as being successful.

Earlier official statements cited a number of reasons for the failures of Bulava tests, including faulty components, attempts to replace specific materials with cheaper substitutes and obsolete manufacturing equipment.

The further development of the Bulava has been questioned by some lawmakers and defense industry experts, who have suggested that all efforts should be focused on the existing Sineva SLBM.

But the military has insisted there is no alternative to the Bulava and said the tests of the missile would continue until it is ready to enter service with the Russian Navy.

Another defense industry source said on Tuesday that Russia could increase the number of Bulava tests in 2010 starting in May-June, and "drastically change the approach to testing procedures."

The Bulava (SS-NX-30) SLBM carries up to 10 MIRV warheads and has a range of over 8,000 kilometers (5,000 miles). The three-stage liquid and solid-propellant ballistic missile is designed for deployment on Borey class nuclear-powered submarines.

MOSCOW, January 12 (RIA Novosti)