GIGLIO, Italy - The vast wreck of the cruise ship Costa Concordia shifted on the undersea ledge supporting it on Friday, forcing a new suspension in rescue work and threatening plans to pump oil out of the vessel to prevent a possible environmental disaster.

Firefighter spokesman Luca Cari said the rescue squads will be discussing the next step after the movement made conditions unsafe for the divers who were already hampered by poor visibility, floating objects and underwater debris.

Seven days after the 114,500-ton ship capsized off the Tuscan coast, hopes of finding anyone alive have all but disappeared and the cold waters around the ship have become rougher with worse weather expected during this weekend.

Attention is now turning to how to remove more than 2,300 ton of fuel aboard the vessel, which lies on its side on a rock shelf in about 20 meters of water off the little island of Giglio and which could slide off its current place.

Salvage crews have been forced to wait for the search for survivors and bodies and only after that search is called off can they begin pumping the fuel out of the wreck, a process expected to take at least two weeks.

Environment Minister Corrado Clini told parliament on Thursday that he had instructed the liner's operator, Costa Cruises, to take all possible measures to anchor the ship to prevent it from slipping further into the sea. 

"If the ship slides, we hope that it doesn't break into pieces and that the fuel tanks do not open up," he said.

Clini said there was a risk that the ship could sink to 50 to 90 meters below the rock ledge on which it is caught, creating a major hazard to the environment in one of Europe's largest natural marine parks. 

Eleven people are known to have died out of more than 4,200 passengers and crew aboard when the ship struck a rock just meters from the shoreline, tearing a large gash in the side of the hull. As many as 24 are still unaccounted for, although that number probably includes bodies found but not yet identified.

Regulation 

The ship's captain Francesco Schettino has been placed under house arrest, accused of causing the disaster and then abandoning ship before the evacuation was complete. 

His lawyer said he has admitted bringing the ship too close to shore but denies sole responsibility and said other factors may have played a role in the accident.

The ship's operators have suspended him and said they considered themselves "the damaged party" in the accident, which industry experts say could turn out to be the biggest maritime insurance claim in history.

On Thursday, SkyTG24 broadcast a tape of what was described as a conversation between coastguard officials and the bridge of the Concordia which appeared to show officers telling authorities they had suffered only a blackout more than 30 minutes after the impact.

In an interview with the daily Corriere della Sera, the chief executive of Costa Cruises criticized Schettino for delaying the order to evacuate and denied that he had faced pressure to wait because of the potential cost to the company.

"I assure you absolutely that no one thought in financial terms. That would be a choice that would violate our ethics," he said. He also denied knowledge of captains sailing dangerously close to shore to provide a spectacle for passengers.

"I can't rule out that individual captains, without informing us, may have set a course closer to land. However I can rule out ever having known that they may have done it unsafely," he said. 

The Italian cabinet will discuss new regulations on Friday to prevent big cruise ships from taking risky routes and passing too close to islands or shorelines.