The MUH-1 Marineone, the Marine variant of the KUH-1 Surion helicopter, crashed at a military airport in the southeastern city of Pohang on Tuesday, killing five of the six Marines aboard and injuring the other.

"With various possibilities in mind and based on scientific grounds, the investigation team will ascertain the cause of the accident in a neutral and objective manner to make sure that there will not be any suspicion left," the Marines said in a statement.

"Upon the completion of the probe, we will inform the bereaved families and citizens of the results transparently. Once again, we extend our words of solace to the deceased fellow troops and their families," they added.

The press briefing came belatedly amid allegations that the government is seeking to downplay the accident apparently to minimize any negative impact on export plans for the homegrown chopper.

Soon after the crash, military authorities said they launched a joint investigation team involving officials from the Marine Corps, Navy, Air Force, Defense Agency for Technology and Quality (DATQ), and the Army's aviation operations command. But on Thursday, it excluded three DATQ employees, citing the possibility of a conflict of interest.

The investigators are said to be putting more weight on technical defects, rather than human error, as the more likely cause of the crash because the chopper's rotor blades were separated from the fuselage just four to five seconds after takeoff.

The Marines received the helicopters in January for transporting its service members and equipment. The MUH-1s are the first major aircraft in the possession of the 28,000-strong troops since they were integrated into the Navy in 1973.

The Marines had planned to introduce a total of 28 Marineones by 2023. Following the accident, the Marine Corps and Army have grounded all Marineones and Surions.

Meanwhile, a former marine, who was recently discharged, said that the ill-fated chopper required maintenance checkups almost every day due to defects. The former marine belonged to a unit that ran the Marineone.

"The second Marineone (that crashed this week) could not be deployed due to defects. Instead, the first Marineone was sent (for a mission)," he told Yonhap News Agency, refusing to reveal his name.

"So when I heard the news report of the accident, I immediately thought that it might be the second Marineone. There was a vibration problem. ... I heard seniors saying it could get into trouble at some point," he added.

Later in the day, Vice Defense Minister Suh Choo-suk met the victims' families to console them and accepted their demand to open the scene of the accident to the press, a ministry official said.

Suh also told the families that his ministry will respect their request for "appropriate treatment and compensation" for the deaths.

Suh apparently met them on behalf of Defense Minister Song Young-moo who was attending a parliamentary session at the time.

The previous day, Song pledged to offer "respectable treatment commensurate with the troops' sacrifices." (Yonhap)