Updated

India's navy on Friday retrieved three badly burned bodies from a submarine that exploded in a Mumbai dockyard and said it was unlikely any of the other 15 missing crewmen would be found alive.

The diesel-powered INS Sindhurakshak sank in a military dockyard early Wednesday, dealing a setback to India's naval ambitions just days after it unveiled its first domestically made aircraft carrier.

Navy divers managed to enter the vessel, whose forward section was totally destroyed in the fire, but their progress was hampered by extreme heat, poor visibility and mangled hatches.

The first bodies were retrieved from a compartment behind the tower Friday and have been sent for DNA testing because severe burns prevented their identification, a navy statement said.

The state of the bodies and conditions within the submarine "leads to the firm conclusion that finding any surviving personnel within the submarine is unlikely", the statement said.

It also suggested some bodies might never be found because of the fierce temperatures generated in the fire during which some of the weapons on board -- cruise missiles and torpedoes -- ignited.

"The navy will continue to search every inch of the submerged submarine till all bodies are either located or it can be stated with finality that no bodies remain to be found," it said.

The navy's focus remains on accessing all compartments of the vessel before attempting to salvage the vessel.

"Salvage of the submarine would only be attempted thereafter for which many alternatives including deploying professional salvers are also being considered," it added.

An inquiry has been set up to determine what caused the blasts, which turned the recently refurbished Russian-built submarine into a fireball.

The Times of India newspaper speculated Friday that sabotage might have been the cause of the explosion, but the navy chief said Wednesday that "the indicators at this point of time do not support that theory".

The families of the 18 men on board at the time of the explosion, whose names have been released, have gathered in Mumbai.

The 16-year-old submarine, whose name means "Protector of the Seas" in Hindi, returned from Russia in April where it underwent a two-year overhaul of its communication, weapons and propulsion systems.

It is still covered by a Russian warranty and the Russian company responsible for the refit, Zvyozdochka, has offered its assistance.

Indian Prime Minister Manmohan Singh, addressing the nation in a traditional Independence Day speech on Thursday, voiced sorrow at the blast.

"The accident is all the more painful because the navy had recently achieved two major successes in the form of its first nuclear submarine, INS Arihant, and the aircraft carrier, INS Vikrant," Singh said.

In addition to the aircraft carrier launched Monday, India announced sea trials for its first domestically made nuclear submarine last weekend, which Singh trumpeted as a "giant stride" for the country.