Divers have found a woman's body in a submerged section of the grounded Costa Concordia, raising the death toll in the cruise liner tragedy to at least 12.

Italian Coast Guard Commander Cosimo Nicastro told The Associated Press that the body, wearing a life jacket, was found in a narrow corridor near an evacuation staging point at the rear of the ship.

The body was taken to Giglio, the Tuscan island where the vessel hit a reef and ran aground on January 14.

Twenty people are still missing.

Cmdr Nicastro said the woman's body was found during a particularly risky search.

"The corridor was very narrow, and the divers' lines risked snagging" on objects in the passageway, he said.

To help the coast guard divers get into the area, Italian navy divers had preceded them, setting off charges to blast holes for easier entrance and exit, he added.

The woman's nationality and identity were not immediately known.

Before the body was found, 21 people were listed as missing, one of them a Peruvian woman crew member, the others passengers.

Three bodies were found in the water near the ship in the first hours after the accident. Since then the other victims have all been found inside the Concordia, apparently unable to get off the ship during a chaotic evacuation via lifeboats and later by helicopters. Some survivors jumped off and swam to safety.

The Concordia hit a reef and ran aground a week ago, while passengers dined, about two hours after the ship had set sail from the port of Civitavecchia on the Tyrrhenian Sea.

Cruise company Costa Crociere has said the captain had deviated without permission from the vessel's course in an apparent manoeuvre to sail close to Giglio to impress passengers.

Search and rescue efforts for survivors and bodies have meant that an operation to remove heavy fuel from the Concordia's tanks has not yet begun, although specialised equipment has been standing by for days.

Today, light fuel, apparently from machinery on board the capsized Costa Concordia, was detected near the ship.

But Cmdr Nicastro said there was no indication that any of the nearly 500,000 gallons (2,200 metric tons) of heavy fuel oil has leaked from the ship's double-bottomed tanks.

He said the leaked substance appears to be diesel, which is used to fuel rescue boats and dinghies and as a lubricant for ship machinery.

There are 185 tons of diesel and lubricants on board the crippled vessel, which is lying on its side just outside Giglio's port.

Cmdr Nicastro described the light fuel's presence in the sea as "very light, very superficial" and appearing to be under control.

Although attention has been concentrated on the heavy fuel oil in the tanks, "we must not forget that on that ship there are oils, solvents, detergents, everything that a city of 4,000 people needs", Franco Gabrielli, the head of Italy's civil protection agency, told reporters in Giglio.

Mr Gabrielli, who is leading rescue, search and anti-pollution efforts for the Concordia, was referring to the roughly 3,200 passengers and 1,000 crew who were on board the cruise liner when it ran into the reef, and then, with sea water rushing into a 230ft (70m) gash in its hull, listed and finally fell on to its side.

Considering all the substances on board the Concordia, "contamination of the environment... already occurred" when the ship capsized, Mr Gabrielli told a news conference.

Vessels equipped with machinery to suck out the light fuel oil were in the area, officials told Italian TV.

Earlier today, crews removed oil-absorbing booms used to prevent environmental damage in case of a leak. Originally white, the booms were greyish.

Divers resumed their search of the wreckage today after data indicated that the ship had stabilised in the sea.

Italian news reports said divers were also trying to locate the captain's safe, in case it might contain documentation useful to the criminal probe.

The Italian captain of Concordia, Francesco Schettino, is under house arrest for investigation of alleged manslaughter, causing a shipwreck and abandoning the ship before all were evacuated.

He insists he helped co-ordinate the evacuation from Giglio's docks after leaving the ship when the Concordia lurched to one side.

The search was suspended yesterday after the Concordia shifted, prompting fears that it could roll off a rocky ledge and plunge deeper into the sea.

An abrupt shift could also cause a leak in the Concordia's fuel tanks, polluting the pristine waters around Giglio, part of a seven-island Tuscan archipelago.