South Korea's Marine commander has expressed readiness to step down, military officials said Thursday, amid criticism that barrack-room bullying triggered a deadly shooting spree this month.

Marine Corps chief Yoo Nak-Joon told Defence Minister Kim Kwan-Jin on Tuesday that he was ready to take responsibility over the rampage that left four soldiers dead and one injured, a ministry spokesman said.

"I will take responsibility if there is something for which I must be responsible," Yoo was quoted as saying.

The elite Corps has also reported several recent suicides, some of them apparently related to bullying.

Yonhap news agency said Yoo had submitted his resignation, but military officials said he was expected to clarify his stance next Monday when the defence minister chairs a meeting of Marine commanders.

The 19-year-old corporal surnamed Kim opened fire on July 4 at his base on Ganghwa Island. He was himself injured by a grenade blast in a suicide attempt after the shooting.

Investigators said an earlier army psychology test had found him to be unstable and to have difficulty coping with military life.

"There should be no more beating or bullying," Kim reportedly said in an interview from his hospital bed, complaining that neither his superiors nor his juniors respected his rank.

A colonel and a lieutenant-colonel from Kim's unit are to be sacked as commanders.

In a separate incident, the defence ministry said a Marine sergeant-major was found dead Thursday but gave no immediate details.

Last Sunday a 19-year-old Marine hanged himself in his barracks in the southeastern port of Pohang. Investigators found an apparent suicide note in his locker with complaints about his life in the military.

An autopsy found signs of subcutaneous bleeding in his chest, an indication that he had been beaten.

Another Marine was found to have hanged himself last week while on a leave of absence. Investigators said he had talked to his friends about the difficulties of military life.

The defence ministry has vowed a crackdown on physical abuse throughout the 650,000-strong mainly conscript military.