South Korea’s ousted president Yoon Suk-yeol was indicted on Friday on allegations he and others tried to manipulate the investigation into a marine's drowning in another criminal case against the ex-leader.

Yoon was removed from office this year after being indicted on a rebellion charge related to his December 3 martial law decree last year that plunged the country into political turmoil.

After taking office in June, new President Lee Jae-myung appointed three independent counsels to investigate Yoon’s martial law imposition and other allegations involving him, his wife and associates.

On Friday, one of the independent counsels charged Yoon, his former defense minister and 10 other figures with abuse of power, alleging they tried to alter an investigation report on the death of Cpl Chae Su-geun, who died during a search-and-rescue operation for flood victims in 2023.

The marine corps' early investigation report held one of the corps' division commanders and seven other people responsible for Chae's death.

But Yoon expressed fury over the commander's inclusion, prompting top presidential and Defence Ministry officials to pressure the marine corps to revise the report to exclude the commander, assistant special counsel Choung Min-young told a briefing.

Park Jung-hun, the head of the marine corps' investigation team, defied the pressure and sent the report to police, but Yoon ordered officials to retrieve the report from police and dismiss Park and investigate him on charges of insubordination, Choung said.

Choung said Park's investigation was conducted in line with law and principle, but Yoon and other indicted “systemically” committed abuse of power that “undermined fairness and independence” of the marine corps' investigation team.

Yoon, who is in jail, has reportedly denied the allegations against him.

The trial over charges that he masterminded a rebellion is ongoing and a verdict may come early next year.

A conviction on that charge carries the possible penalty of capital punishment or life imprisonment.

Yoon was indicted this month on charges alleging he ordered drone flights over North Korea to deliberately create military tensions and justify martial law. (AFP)