SEOUL -- South Korea's prosecution indicted arrested President Yoon Suk-yeol on an insurrection charge, multiple media outlets reported on Sunday.

Yoon was put on trial in custody as the suspected ringleader of insurrection, becoming the country's first incumbent president to be formally arrested and indicted.

Yoon was accused of conspiring with former Defense Minister Kim Yong-hyun, who had already been indicted under detention, to declare unconstitutional, illegal martial law and dispatch armed forces into the National Assembly.

After receiving Yoon's case from the anti-corruption agency, the prosecution requested Yoon's extended arrest twice for supplementary investigation, but the Seoul Central District Court repeatedly rejected it to bring Yoon to trial as early as possible.

A warrant to keep Yoon in custody for up to 20 days, including the arrest period, was issued by another Seoul court on Jan 19.

Yoon was apprehended in the presidential office on Jan 15.

The motion to impeach Yoon was passed through the National Assembly on Dec. 14 last year and was delivered to the constitutional court to deliberate it for up to 180 days, during which Yoon's presidential power is suspended.

Yoon declared an emergency martial law on the night of Dec 3. It was revoked by the National Assembly hours later.