MOSCOW, November 8 (RIA Novosti) - Events in memory of 20 people killed in an accident during tests of the Nerpa nuclear attack submarine will be held on Sunday in Russia's Far East.

On November 8, 2008, while the Nerpa was undergoing sea trials, its onboard fire extinguishing system went off, releasing a deadly gas into the sleeping quarters. Three crewmembers and 17 shipyard workers were killed. There were 208 people, 81 of them submariners, aboard the vessel at the time.

A monument to 12 residents of the Far Eastern city of Komsomolsk-on-Amur, who were killed in the deadly accident, will be opened at the city's cemetery.

About 200 people will gather to observe a minute of silence in the Far Eastern town of Bolshoy Kamen, home to three victims of the incident.

The submarine has undergone a range of sea trials since early July. The final state tests will begin later this month, after which the Nerpa will enter service with Russia's Pacific Fleet in and will then be leased out to the Indian Navy.

"No serious damage was done to the [submarine's] compartment. After the accident, we checked all equipment and cleaned the compartment. We also changed the Freon gas [in the fire suppression system]," an official with the Amur shipyard said.

Costs of repair are estimated at $65.6 million.

India reportedly paid $650 million for a 10-year lease of the 12,000-ton K-152 Nerpa, an Akula II class nuclear-powered attack submarine.

Akula II class vessels are considered the quietest and deadliest of all Russian nuclear-powered attack submarines.