The official results of a probe into the latest failure of Russia's ill-fated Bulava ballistic missile are ready and have been sent to the government for review, a defense industry source said on Tuesday.

The latest unsuccessful launch of the missile, which Russia hopes will be a key element of its nuclear forces, took place from the Dmitry Donskoy nuclear submarine in the White Sea in early December 2009. Only five of 12 Bulava launches have been officially reported as successful.

"The conclusions [of the investigation commission] are ready and they are on their way to the government," the source said.

Russia has postponed test launches of the troubled Bulava ballistic missile until November this year.

The Russian Navy earlier planned at least four new test launches of the missile at the end of June, but defense industry experts suggested they would need to build three missiles under identical conditions to establish the causes of the failures.

The Bulava (SS-NX-30) is a three-stage liquid and solid-propellant submarine-launched ballistic missile (SLBM). It carries up to 10 MIRV warheads and has a range of over 8,000 kilometers (5,000 miles).

The missile has been specifically designed for Russia's new Borey class nuclear submarines.

The future development of Bulava has been questioned by some lawmakers and defense industry officials who suggest that the Russian Navy should keep using the more reliable Sineva SLBM.

The Russian military has insisted that there is no alternative to the Bulava and pledged to continue testing the missile until it is ready to be deployed with the Navy.