South Korea's Yoon appears in court for first criminal trial hearing

Impeached South Korean president Yoon Suk-yeol has appeared in court for a hearing where his lawyers contested his arrest on a criminal charge alleging he was orchestrating a rebellion when he briefly imposed martial law in December.

Security was heightened on Thursday as the motorcade transporting Yoon arrived at the Seoul Central District Court, and dozens of his supporters rallied nearby.

The preliminary hearing will involve discussions of witnesses and other preparations for his criminal trial, and the court was also to review the request by Yoon's lawyers to cancel his arrest and release him from custody. Such challenges are rarely successful.

Yoon was indicted January 26 on the rebellion charge carrying a potential punishment of death or life in prison. In South Korea, presidents have immunity from most criminal prosecutions, but not on charges of rebellion or treason.

The indictment alleges his imposition of martial law was an illegal attempt to shut down the National Assembly and arrest politicians and election authorities. The conservative Yoon has said his martial law declaration was intended as a temporary warning to the liberal opposition and that he had always planned to respect lawmakers' will if they voted to lift the measure.

Yoon's lawyer Kim Hong-il described the trial as a "significant event in constitutional history".

"The judiciary must serve as the stabilising force," he told the court, warning that he was "witnessing a reality where illegality compounds illegality".

He urged the court to "ensure that the defendant's rights are not unjustly violated".

Yoon's fate in balance

Yoon's presidential powers were suspended when he was impeached December 14, and South Korea's Constitutional Court is nearing a decision on whether to formally remove him from office or dismiss the Assembly's impeachment and reinstate him.

That process could take up to a fortnight or even longer.

Previously impeached presidents Park Geun-hye and Roh Moo-hyun had to wait 11 and 14 days, respectively, to learn their fates.

If Yoon is removed from office, the country must hold fresh presidential elections within 60 days.

Martial law was lifted about six hours after Yoon declared it but has caused political turmoil, disrupted high-level diplomacy and tested the resiliency of the country's democracy.

Yoon's conservative supporters rioted at the Seoul Western District Court after it authorised his arrest last month, while his lawyers and ruling party have openly questioned the credibility of courts and law enforcement institutions handling the case.