Lee Joon-Seok (C), captain of the South Korean ferry "Sewol" which sank at sea off Jindo, is investigated at Mokpo police station in Mokpo April 17, 2014.[Photo/Agencies]

The Coast Guard has been questioning the ship's captain and other crew members to determine what went wrong. Coast Guard officials said they found that the ill-fated ship deviated from a government-recommended route.

"(The ferry) took a path slightly different from the route recommended by the Ministry of Maritime Affairs and Fisheries," Koh Myung-seok, a senior Coast Guard official, told a press briefing in Seoul.

Koh, however, said it is premature to conclude that the ferry had deviated based on a track chart.

The ship also made a sharp turn although it is supposed to make a gradual turn, Coast Guard officials said. The loud thud before the sinking could be from cargo shifting from the turn, experts said.

The government has come under strong fire over its handling of the disaster. It has even been unable to figure out exactly how many people were aboard the ship, and it revised the figure, as well as the numbers of those rescued and missing, many times.

Survivors also blamed the ship's crew, saying they were repeatedly told to stay put where they were, even when the ship began tilting. Had they been told to evacuate earlier, more people would have survived the disaster, they said.

Reports say the ship's captain was one of the first to leave the vessel.

The Coast Guard officials said that they are questioning the 69-year-old captain, surnamed Lee, to investigate safety and rescue conditions aboard the ferry.

"I am sorry for passengers and family members of the missing," Lee told reporters before entering the Coast Guard office.

A total of 325 passengers were students from Danwon High School in Ansan, just south of Seoul. They were on a school trip to Jeju, and 245 students remain unaccounted for.

The nine dead included four 17-year-old students and a 25-year-old teacher from the high school, as well as a 22-year-old female crew member. But the identities of the other three were not immediately known.

Among the rescued passengers include two Filipinos, a 40-year female surnamed Cabrsa and a 45-year-old male surnamed Manio, said a government official.

The official added that an 18-year-old Russian, only identified by his surname Serkov, is listed as one of the missing passengers. Serkov is a student at Danwon High School, he added.

Meanwhile, the official said the government is in the process of confirming whether two Chinese nationals were on board as the Coast Guard could not identify them by checking the personal information passengers provided while purchasing tickets.

Police, meanwhile, are trying to check the authenticity of an alleged text message sent to one of the missing students' family members claiming that several people have survived in an air pocket of the capsized ferry, officers said.

The police, however, said they are not ruling out the possibility that the message could have been sent by someone as a prank.

The ship, which plies between Incheon and Jeju twice a week, was built in Japan in 1994, is 146 meters long and 22 meters wide, and has the maximum capacity of carrying 921 people, 180 vehicles and 152 shipping containers at the same time.

The United States expressed its condolences to the families of those killed.

"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, she said.

On Wednesday, the US military send an amphibious assault ship equipped with two helicopters to the scene to help with the search and rescue operations. The ship was on its routine patrol mission in the western sea.

UN Secretary General Ban Ki-moon also expressed condolences and sympathy for the victims.

Families face agonising wait	Two Chinese nationals aboard ship