The South Korean president has said that the behaviour of the captain and crew of the capsized ferry with 476 people on board was unacceptable and "tantamount to murder".
"The actions of the captain and some crew members were utterly incomprehensible, unacceptable and tantamount to murder," President Park Geun-hye was quoted as saying in a meeting with senior aides on Monday.
"Not only my heart, but the hearts of all South Koreans have been broken and filled with shock and anger."
The ferry Sewol sank in 27m of water in calm seas on Wednesday as it sailed from Incheon in the northwest to the southern island of Jeju.
Lee Joon-seok, the captain, was arrested on Saturday along with a helmsman and the ship's relatively inexperienced third officer, who was in charge of the bridge when the ship first ran into trouble.
Four more crew members were arrested on Monday, Al Jazeera's Adrian Brown reported from the island of Jindo in South Korea's southwest.
|Adrian Brown reports from Jindo
Park said it was increasingly clear that Lee had unnecessarily delayed the evacuation of passengers from the Sewol as it started sinking, and then "deserted them" by escaping first.
"This is utterly unimaginable, legally and ethically," she said, adding that all parties to the disaster, from the owners, to the safety inspectors to the crew would be investigated and all those responsible would be held "criminally accountable".
Park had been heckled on Thursday when she met relatives of the hundreds of passengers still missing - most of them schoolchildren.
The families have criticised the official response to the disaster, saying the initial rescue effort was inadequate and mismanaged.
Of 476 people on board, 64 have been confirmed killed and 238 people are still missing.
Grieving relatives of the missing ferry passengers staged a violent protest on Sunday against a South Korean minister, venting their frustration over what they alleged was tardy rescue operation.
A relative of a missing passenger pulled the hair of Lee Ju-young, the minister in charge of the ocean policies, as he walked to the families at the port in Jindo, where the bodies are being brought out of the sea.
Others shouted at him, saying the government has not come up with a concrete rescue plan and has failed to find survivors among those missing.
A transcript released on Sunday shows that the Sewol was crippled with confusion and indecision well after it began listing dangerously.