India on Wednesday said its naval submarine, Sindhurakshak, was completely destroyed in a fire triggered by an explosion in the southern port city of Mumbai resulting in the death of several sailors onboard the underwater vessel. \"I feel sad ... about those navy personnel whom lost their lives in the service of the country,\" Defence Minister A.K. Antony told reporters outside parliament in New Delhi. He did not specify how many sailors were killed in the submarine accident. Around 18 sailors, including three officers, were on board the marine, official sources said. The minister described the submarine explosion as one of the worst tragedy in recent Indian history. Giving details about the incident, the defense ministry stated that an explosion caused a major fire on board INS Sindhurakshak, a Kilo-class submarine of the Indian Navy, shortly after midnight on 14 August 2013. \"Fire tenders from the Naval Dockyard as well as the Mumbai Fire Brigade were immediately pressed into action. Due to as yet unknown damage suffered as a result of the explosion, the submarine has submerged at her berth with only a portion visible above the surface,\" the defense ministry release added. The 2,300 tonne conventionally powered submarine had returned after an upgrade in Russia, some three months ago, official sources revealed, adding, the submarine was capable of carrying a potent weapons. Soon after the incident, Navy chief Admiral D K Joshi left for Mumbai. \"A Board of Inquiry has been instituted to investigate into the causes of the accident,\" defense ministry said.