SEOUL — Ousted South Korean President Yoon Suk-yeol became the country's first sitting head of state to stand trial in a criminal case as hearings opened on Thursday regarding his bid to impose martial law.

Traveling around Seoul in a prison transport vehicle, Yoon appeared in two different courts on Thursday, contesting his arrest on rebellion charges in one and fighting an effort to remove him from office in the other. Both cases — one on criminal charges, one on impeachment — are related to his imposition of martial law.

Last month, prosecutors indicted Yoon after accusing him of leading an insurrection with his short-lived imposition of martial law on Dec 3.

Security was heightened at the Seoul Central District Court as the motorcade transporting Yoon arrived for a preliminary hearing that involved discussions of witnesses, proposed evidence and other preparations for his criminal trial.

Prosecutors called for swift proceedings considering the gravity of the case, but Yoon's lawyers said they needed more time to review records.

Yoon had "no intention to paralyze the country", one of his lawyers told the court, adding that his martial law declaration aimed to tell the public of the "legislative dictatorship of the huge opposition party".

If convicted, Yoon could face years in prison for his martial law decree, which shocked the country and sought to ban political and parliamentary activity and control the media.

The move unleashed political upheaval in Asia's fourth-largest economy, with the prime minister also impeached and suspended from power, while top military officials were indicted for their role in the matter.

The court also heard a bid by Yoon's lawyers to cancel his detention, saying the matter had been investigated in an illegal manner, and that there was no risk of Yoon trying to destroy evidence.

It was unclear when the court would rule on the detention, but a judge set the next hearing of the criminal case for March 24.

After the criminal case, Yoon also attended on Thursday afternoon a parallel impeachment trial by the Constitutional Court that has entered its final phase.

The court's acting chief justice Moon Hyung-bae said on Thursday that the next hearing will be held on Tuesday, during which Yoon and the parliament, which is presenting the case against him, will give final remarks.

On Thursday, witnesses testifying to the court included Prime Minister Han Duck-soo, who has also been impeached and awaits the court's decision on his fate.

The Constitutional Court is reviewing parliament's impeachment of Yoon on Dec 14 and will decide whether to remove him from office permanently or reinstate him.

Analysts have said a March ruling is likely.

If Yoon is removed, a new presidential election must be held within 60 days.

Agencies Via Xinhua