The United States is sending a Navy salvage ship to help South Korea with the recovery of the ferry that capsized last week.
South Korea has not formally requested the ship, but the USNS Safeguard was being moved from Thailand toward South Korea in case it does, Pentagon spokesman Colonel Steve Warren said.
The 78-metre ship is designed to salvage or repair ships crippled in combat anywhere in the world.
It can lift, tow and conduct diving operations.
An amphibious assault ship, the USS Bonhomme Richard, is already taking part in rescue operations off the southwestern coast where the Sewol sank on Wednesday with 476 people aboard, including 352 high school students on a holiday trip.
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At least 87 people are confirmed dead and 215 remain unaccounted for.
"Helicopters from the Bonhomme Richard flew search and rescue operations yesterday," Warren said.
A US Navy engineer and master diver also were helping out aboard a South Korean navy ship, he said.
More than 500 divers have come from all over South Korea, most of them civilian volunteers but also from the military, to join the rescue operations.
