South Korea's parliament presses for Yoon's removal as impeachment trial winds down

South Korean President Yoon Suk Yeol could try to impose martial law again or undermine constitutional institutions should he be reinstated, lawyers for parliament argued on Tuesday as his impeachment trial entered its final phase.

After weeks of testimony by high-ranking current and former officials, including some facing criminal charges for their role in the brief imposition of martial law on December 3, lawyers for both sides summarised their arguments and evidence at the Constitutional Court.

"Declaring martial law in a situation that doesn't fit a national emergency is a declaration of dictatorship and military rule," Kim Jin-han, a lawyer for the parliament, told the justices.

He cited pro-Yoon protesters who stormed a different court in January.

"If he returns to work, we don't know if he will again exercise martial law," Kim said. "If he returns to work, we can't rule out the possibility that he will attack other state and constitutional institutions."

The Constitutional Court is due to hold another hearing to question three more witnesses on Thursday, including the impeached prime minister and the former police chief.

The court is reviewing parliament's impeachment of Yoon on December 14 and will decide whether to remove him from office permanently or reinstate him. If he is removed, a new presidential election must be held within 60 days.

Yoon has argued that he had a right as president to issue his martial law decree, which lasted around six hours before he rescinded it in the face of parliamentary opposition. He said the move was also justified by political deadlock and threats from "anti-state forces" sympathetic to North Korea.

His case at the Constitutional Court has also included arguments that he never actually intended to stop parliament from operating, even though the order was publicly declared and troops and police were deployed to the legislature.

Yoon also sent troops to the National Election Commission and later said the decree was necessary in part because the NEC had been unwilling to address concerns over election hacking, a claim rejected by election officials.

Prosecutors have also indicted Yoon on separate criminal charges of leading an insurrection. He was arrested last month and is being held at a detention centre.

The first preparatory hearing in that case is scheduled for Thursday.

Insurrection is one of the few criminal charges from which a South Korean president does not have immunity. It is punishable by life imprisonment or death, although South Korea has not executed anyone in decades.