Russia will lease a nuclear powered submarine to India before October, a Russian Navy Staff admiral said.

Previous media reports said that the K-152 Nerpa attack submarine had already been transferred to India on a 10-year lease.

"The submarine is completely ready for transfer. An Indian crew is currently training aboard with Russian instructors," the admiral - who requested anonymity - said.

The training course includes the launching of cruise missiles, he added.

"This should be completed before October: We're running late as it is," the admiral said.

Twenty sailors were killed onboard the submarine as the K-152 Nerpa was undergoing sea trials in the Sea of Japan in November 2008. A fire extinguishing system malfunctioned leading to the discharge of a toxic gas.

The boat is now fully operational after repairs.

The $900-million lease contract was drawn up after Moscow and New Delhi struck a deal in January 2004 where India agreed to fund part of the Nerpa's construction.

The Nerpa was originally scheduled to be inducted into the Indian Navy as INS Chakra by mid-2008.