SEOUL -- An unidentified man burned himself to death Wednesday near South Korea's Corruption Investigation Office for High-ranking Officials (CIO) building in Gwacheon, just south of Seoul, Yonhap news agency said citing the police.

The man set himself on fire at around 8:05 p.m. local time (1105 GMT) in a green area near the CIO office. He was taken to a hospital by firefighters but eventually died.

The police were checking the man's identity and investigating the exact circumstances of the accident based on the testimony of witnesses.

It came hours after South Korean President Yoon Suk-yeol was arrested in the presidential residence in central Seoul and moved to the CIO office for questioning over his short-lived martial law imposition.

Yoon became the country's first sitting president to be kept in custody.

The CIO will be required to decide within 48 hours whether to seek a separate warrant to detain Yoon for up to 20 days for further questioning or release him.

Yoon, who was named by investigative agencies as a suspected ringleader on an insurrection charge, declared martial law on the night of Dec. 3 last year but it was revoked by the National Assembly hours later.

The impeachment motion against Yoon was passed in the National Assembly on Dec. 14 and delivered to the constitutional court to deliberate it for up to 180 days, during which Yoon's presidential power will be suspended.