MUMBAI  - India's navy retrieved Friday four burnt bodies from a submarine that exploded in a Mumbai dockyard, and said it was unlikely any of the remaining 14 missing crewmen were 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 destroyed in the fire, but their progress was hampered by extreme heat, poor visibility and mangled hatches. The first bodies were retrieved from the most easily accessible compartments 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 personnel 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.

Water inside the craft was still too hot for divers to enter 12 hours after the accident on Wednesday, and visibility inside was nil "even with high power underwater lamps". "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," the statement said. "The body count is now four," a navy spokesman told AFP. Senior navy officers also spoke of difficulties in pumping out seawater from the Russian-origin submarine and said the "top priority" was to refloat the mangled vessel.

"The divers who are being sent in one by one are also in great peril because of jagged metal and the distorted hull," navy spokesman D.K. Sharma said.

Others said the only possible way to recover the bodies of the missing crew inside the hull was to raise it.

"Thinking at the highest level is that the top priority must be to bring her up from sea bed as it is vital to access the human remains because family members are distraught," a senior officer said, asking not to be named.

"Besides, it will also help a board of enquiry which has been ordered into the disaster," he added.

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

"The navy is not a salvage company so the option of (enlisting) a specialised international company to bring it up is also on the mind of the navy," the officer added.

The inquiry will seek to determine what caused the blasts, which turned the recently refurbished Russian-built submarine into a fireball.

While some media reports have suggest sabotage might have caused the blast, the navy chief said Wednesday that "the indicators at this point of time do not support that theory".

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.