SEOUL -- South Korea's constitutional court started the first preparatory hearing Friday for a trial on President Yoon Suk-yeol's impeachment that was passed by the parliament earlier this month over Yoon's short-lived martial law imposition.

The pre-trial hearing began at about 2:15 pm local time to let legal representatives of both Yoon and the National Assembly submit the lists of witnesses and evidence and adjust dates for future proceedings.

The National Assembly was represented by the chief of the legislation and judiciary committee and other lawyers, while Yoon's side appointed a team of defense counsels hours before the preparatory hearing.

Yoon insisted that his martial law declaration was an act of governance, but the National Assembly called it an act of insurrection.

The impeachment motion against Yoon was passed by 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.

Yoon declared an emergency martial law on the night of Dec 3 but it was revoked by the National Assembly hours later.