"The boat is now on shipyard sea trials. I don't think it will be put in service this year, that will take place in 2013. It still has to complete state acceptance trials in the White Sea," said Defense Ministry State Orders department head Andrei Vernigora.

"Also, there were delays with construction by the main contractor and subcontractors. All this led to delays, so we are late now," he said.

In August, the boat's maker Sevmash said it hoped to hand the Severodvinsk over to the navy at the end of 2012.

Severodvinsk carried out a series of cruise-missile firings earlier this week including launch of a supersonic cruise missile at a land target.

The Severodvinsk, laid down in 1993, is one of eight Yasen-class boats being built for the Russian Navy.

The multirole attack submarine has a submerged displacement of 13,800 tons, length of 119 meters, speed of 31 knots, and can dive to 600 meters. It has a crew of 90 including 32 officers.

Its main armament consists of 3M55 Oniks (SS-N-26) and 3M54 (SS-N-27) Kalibr cruise missiles and conventional torpedos, rocket-torpedos and mines.