The captain of a cruise ship that ran aground off Italy made an "unapproved, unauthorised" deviation in course, the vessel's owners say.
Costa Cruises boss Pier Luigi Foschi accused Capt Francesco Schettino of sailing too close to a nearby island in order to show the ship to locals.
The captain blamed the crash on rocks that he said were not on his chart.
Six people died and 29 are said to be missing after the Costa Concordia's hull was torn open on Friday.
The authorities earlier said the number of missing was down to 16, but local officials in Grossetto prefecture said late on Monday they had confirmed 25 passengers and four crew remained missing.
German media have reported that 12 German passengers are still missing, and US officials have appealed for information about two Americans who were believed to be on board. Six Italians, two French couples and a Peruvian are also reported to be unaccounted for.
Rescuers continued their search for survivors on Monday, though their work was interrupted for several hours because bad weather had caused the ship to move.
Officials said they would not continue searching overnight.
Capt Schettino is being detained on suspicion of manslaughter.
At an emotional news conference in Genoa, Mr Foschi fought back tears as he apologised for the accident.
"The company will be close to the captain and will provide him with all the necessary assistance, but we need to acknowledge the facts and we cannot deny human error," he said.
"This route was put in correctly. The fact that it left from this course is due solely to a manoeuvre by the commander that was unapproved, unauthorised and unknown to Costa.
"He wanted to show the ship, to [go] nearby this island of Giglio, so he decided to change the course of the ship to go closer to the island."
Some of the passengers on board the ship described hearing a horrendous noise as the ship struck rocks at about 21:30 (20:30 GMT) on Friday.
There were scenes of panic as alarms sounded soon after and the ship began to list. Capt Schettino steered the vessel closer to land to where it now lies on its side just metres off Giglio island.
Some of the passengers and crew were forced to swim for land as the angle of the ship made boarding life boats impossible.
The 4,200 passengers and crew on board had not conducted an emergency drill after leaving on its cruise several hours earlier.
The shipping newspaper Lloyd's List said it had been able to trace the course of the Concordia though information from satellites.
The paper issued a graphic comparing Friday's sailing with an earlier sailing by the liner, suggesting that Friday's route had deviated far from its usual course.
Early on Monday, rescue crews found a sixth body, that of a male passenger.
The BBC's Matthew Price says the ship sank lower in the water during the course of the day.
He says divers have told him that it is dark and difficult to see inside the ship, and that it is disorientating swimming along corridors that have been turned on their side.
Worries are growing that the ship could cause an environmental disaster if it breaks up and sheds its load of about 2,300 tonnes of fuel.
Italian Environment Minister Corrado Clini said there was evidence that liquid was leaking from the ship, but he could not confirm whether the fluid was fuel.
He said the government would declare a state of emergency to release extra funding to avoid a fuel spill.
- Divers describe scene in cruise liner 03:26
- Aerial video shows gash in hull 00:38
- Captain: Rocks not detected 01:07
- Explosives used in search for missing 01:43
- Why the captain changed course 02:04
- How cruise ship deviated from route 03:15
- Night vision footage of ship rescue 04:18
- Cruise ship dancer: 'Absolute panic' 04:21
Capt Schettino, 52, has worked for Costa Cruises for 11 years, and the firm said he had passed all the required courses.
He has denied any wrongdoing, saying the rocks his ship hit were not marked on his nautical chart.
And he also denied claims by prosecutors that he left the Costa Concordia before evacuation was complete, insisting that he and his crew were the last to leave the ship.
First officer Ciro Ambrosio has also been detained.