Impeached President Yoon Suk Yeol attends the impeachment trial at Constitutional Court, Seoul, Jan. 21. Joint Press Corps

President Yoon Suk Yeol on Tuesday denied that he ordered troops to "drag out" lawmakers from the National Assembly after declaring martial law last month, in his first appearance at his impeachment trial at the Constitutional Court.

Yoon was asked by acting court President Moon Hyung-bae whether he had ordered military commanders to drag out lawmakers to stop them from voting down his Dec. 3 martial law decree.

"No," he replied. "(A parliamentary vote) is not something that can be blocked by blocking or delaying it."

The president denied that he gave a note to Finance Minister Choi Sang-mok on the day of the martial law imposition to ask him to draw up a budget for an "emergency legislative body."

He also sought to clarify claims that election fraud was a key reason for his declaration of martial law, saying he simply gave orders to screen the computer servers of the National Election Commission amid suspicions about fair elections.

Yoon arrived at the court in a convoy escorted by the Presidential Security Service from the Seoul Detention Center in Uiwang, just south of the capital, where he has been held in custody since last Wednesday.

At 2 p.m., he entered the courtroom, dressed in a suit and red tie, and sat waiting for the eight justices to arrive for the third hearing of the trial deliberating his impeachment over his declaration of martial law.

"It's my first time attending today, so I will speak briefly," Yoon said while seated after asking Moon for a chance to speak.

"Since coming of age, I have lived with a firm belief in liberal democracy until this very day, and especially during my time in public service," he said.

"As the Constitutional Court is an institution that exists to defend the Constitution, I ask the justices to consider me favorably in various respects."

Yoon is the first president to attend his or her own impeachment trial as former Presidents Roh Moo-hyun and Park Geun-hye were absent from theirs.

Yoon was impeached by the National Assembly on Dec. 14 and remains suspended from duty while an investigation is under way into charges he led an insurrection and abused his power through his declaration of martial law.

Supporters of impeached President Yoon Suk Yeol gather near the Constitutional Court in Seoul, Jan. 21. Yonhap

The Constitutional Court has 180 days from the day it received the case on Dec. 14 to uphold the impeachment and remove him from office or dismiss the impeachment and reinstate him.

If Yoon is ousted, the country will be required to hold a snap presidential election within 60 days.

During the hearing, which lasted 1 hour and 43 minutes, Yoon's legal team denied he had any plans to execute the martial law decree under which all political activities were banned, and all media and publications were subject to the control of the martial law command.

"The decree was drafted by (then Defense Minister) Kim Yong-hyun, and reviewed and revised by the defendant in order to satisfy the outward appearance (of martial law)," Chah Kee-whahn, one of the lawyers, said.

"Strictly speaking, the decree was aimed at prohibiting illegal acts by the National Assembly and not at all at dissolving the Assembly or prohibiting its regular activities," he said.

Yoon has justified his short-lived imposition of martial law as an "act of governance" meant to defend the country from "anti-state forces" and warn the opposition party against abusing its legislative power.

Chah said the deployment of troops to the Assembly during the six-hour enforcement of martial law was aimed at informing the public of parliament's "dangerous behavior" and preparing against a sudden surge of people there.

He flatly denied allegations Yoon ordered the arrest of prominent politicians and judges, including then ruling party leader Han Dong-hoon and Assembly Speaker Woo Won-shik.

Outside the court, hundreds of people gathered to show their support for the president, holding up signs that read "Impeachment Invalid."

Police surrounded the court's perimeter and beyond, and parked buses along sidewalks to prevent any violence among protesters.

One woman was apprehended after assaulting a police officer.

In a neighborhood across the road from the court, 4,000 people attended a conservative rally in support of the president.

Yoon's appearance at the court was the first time he appeared in public since the day he imposed martial law. (Yonhap)