South Korean police said Wednesday that security guards were blocking a raid on President Yoon Suk-yeol's offices to investigate his brief imposition of martial law, with the opposition party accusing the presidential staff of illegally protecting an insurrectionist.

Yoon is already banned from foreign travel as part of an "insurrection" probe into his inner circle over the dramatic events of December 3-4 that stunned South Korea's allies.

Several hours into a standoff at the presidential offices, police Wednesday evening said "The special investigation team is currently continuing to discuss the seizure and search of the presidential office (with the presidential staff and security)."

The main opposition Democratic Party warned it would file legal complaints for insurrection against the presidential staff and security if they continued to obstruct law enforcement.

"What the presidential office (staff) and the security are protecting right now is not the head of state, but an insurrectionist," said DP lawmaker and spokesperson Jo Seung-lae. (AFP)