[Update: Aug. 14, 04:35 p.m., EDT] India’s Defense Minister A.K. Antony confirmed at least some of the 18 sailors on board the Indian navy submarine were killed in the explosion and subsequent fire, news reports said. He expressed condolences, but did not reveal any other details, or the exact number of those killed.

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An Indian navy submarine, INS Sindhurakshak, with an 18-member crew on board exploded, in the early hours of Wednesday, at its home port in the western Indian city of Mumbai, resulting in a major fire on board, the navy said in a statement.

The damage caused by the explosion on board the Kilo-class submarine -- a name used to denote naval diesel-electric submarines made in Russia -- is yet to be determined and the vessel remains submerged at its berth with only a portion visible above the surface, the statement said.

Firefighting apparatus from the naval dockyard and the Mumbai Fire Brigade have been involved in rescue activities, the navy said.

“Efforts are on to ascertain the safety of the personnel and salvage of the submarine,” the navy said, adding that an investigation has been launched into the cause of the accident.

The damage to the submarine has dealt a significant blow to the navy, after the defense ministry spent about $80 million on upgrading the vessel in Russia three months ago, NDTV reported.

Deputy chief of Mumbai’s fire office, P.S. Rahandale, said he heard the explosion on shore while he was near the Gateway of India promenade, which is close to the naval dockyard, and alerted the fire brigade and other emergency services.

Footage aired on television channels and photos captured by people on shore showed a large fireball over the dock where the vessel was berthed.

The accident closely follows India’s announcement on Aug. 10 that it has activated the nuclear reactor on board its nuclear submarine, INS Arihant, the country’s first indigenous nuclear-powered sub. India also upgraded and relaunched its first aircraft carrier, INS Vikrant, on Monday.