(IDEX Online) - Three people died and two were injured after a release of methane gas at Russia's biggest diamond mine.A criminal investigation is taking place into a possible violation of safety rules at Alrosa's Udachny deposit, in the Daldyn-Alakit kimberlite field, Yakutia.A commission led by a representative of Rostekhnadzor, Russia's Federal Service for Environmental, Technological and Nuclear Supervision, is also investigating the circumstances.Operations resumed shortly after the accident, which was reported on 26 November by the Russian news agency Interfax.Alrosa said: "An examination of all workings, including dead-end mines, showed that the concentration of flammable gases was within safe limits."The company's general director Pavel Marinychev said victim's families would receive financial assistance.In August 2012 two people working on the construction of an Alrosa mine, also in Yakutia, also died in a methane gas incident.Pic of Udachny mine, courtesy Alrosa