The U.S. government expressed its condolences Wednesday to the families of those who were killed in the sinking of a South Korean ferry.

"We extend our deepest condolences to the loved ones of those who lost their lives on board the South Korea ferry, the Sewol,"

Marie Harf, the State Department's deputy spokeswoman said at the start of a daily press briefing.

She described the incident as a "terrible tragedy."

The United States is ready to provide any assistance needed in the ongoing search-and-rescue efforts, Harf added.

At least six people were dead, with 290 others unaccounted for, as the 6,825-ton Sewol sank off the Southwestern coast of the country Wednesday morning (local time), according to officials there. It was carrying 475 passengers and crew members en route to the Jeju island from Incheon, west of Seoul. Among them, 179 have been plucked to safety.

A massive search operation is under way, led by military dive teams.

The U.S. 7th Fleet has also joined the operation.

"The USS Bonhomme Richard has moved to the area to assist the government of South Korea with the search and rescue operations...

We are ready to help in any way we can," Harf said. (Yonhap)