Gregorio Borgia, Associated Press
Italian firefighters scuba divers approach the cruise ship Costa Concordia leaning on its side, the day after it ran aground off the tiny Tuscan island of Giglio, Italy, Sunday, Jan. 15, 2012. A helicopter on Sunday airlifted a third survivor from the capsized hulk of a luxury cruise ship 36 hours after it ran aground off the Italian coast, as prosecutors confirmed they were investigating the captain for manslaughter charges and abandoning the ship.

ROME — Rescue crews say a rescue operation on a cruise ship that ran aground and capsized off Tuscany has been suspended after the Costa Concordia shifted a few inches (centimeters) in rough seas.

Fears are mounting that if the ship shifts significantly, the 500,000 gallons of fuel may begin to leak into the pristine waters around the island of Giglio.

Fire department spokesman Luca Cari said the ship had shifted a few centimeters vertically and horizontally Monday because of the seas. He said an underwater search for 16 people still unaccounted for from the 4,200 on board was suspended immediately.

Six people were killed when the ship ran aground Friday. Costa has said the captain, who has been jailed, made an unauthorized deviation from the ship's planned course.