The preparatory hearing for the trial on President Yoon Suk Yeol's impeachment takes place at the Constitutional Court in central Seoul, Dec. 27. Yonhap

The Constitutional Court said Friday it would swiftly proceed with President Yoon Suk Yeol's impeachment trial as it wrapped up the case's first hearing, with the next hearing on the trial set for Jan. 3.

The court made the announcement during the preparatory hearing for the trial on the validity of Yoon's impeachment by the National Assembly this month over his failed imposition of martial law on Dec. 3.

"The case on the president's impeachment is more important than any other case," Justice Cheong Hyung-sik, one of the judges for the preparatory proceedings, said, noting the court first deals with cases that are "most urgent."

"The date was decided by considering the seriousness and gravity of the impeachment trial's impact on state affairs and the public," Justice Lee Mi-son, another Constitutional Court judge, said, referring to the date of next hearing.

The hearing brought together the legal representatives of both Yoon and the National Assembly for the first time to lay out their cases, present their list of witnesses and evidence, and coordinate the dates of future proceedings.

Yoon, who was not required to attend the hearing, did not appear as expected.

During the hearing, Yoon's lawyers said they would dispute the legality of the request for the impeachment trial, apparently referring to possible procedural issues regarding Yoon's impeachment motion at the National Assembly.

The Constitutional Court in Seoul is seen in this Dec. 26 photo. Yonhap

Meanwhile, they acknowledged Yoon's declaration of martial law and the announcement of its decree as fact but said they would later clarify details surrounding the background of the declaration.

Until Friday morning, Yoon had refused to accept documents related to his trial and failed to appoint a legal defense team to handle the case.

With only hours to go, however, his representatives announced the appointment of a team comprised of lawyers Bae Bo-yoon, Yun Gap-geun and Bae Jin-han. Bae Bo-yoon was a Constitutional Court spokesperson during the impeachment trial of former President Geun-hye.

Meanwhile, the National Assembly was represented by former Constitutional Court Justice Kim Yi-su and former National Human Rights Commission Chairman Song Doo-hwan, among others.

Yoon has denied charges he incited an insurrection by declaring martial law on Dec. 3, arguing it was an "act of governance" and a warning against what he described as an abuse of legislative power by the main opposition Democratic Party.

Yoon has also ignored repeated summonses by a joint investigation team to appear for questioning on the insurrection charges.

The court has 180 days to decide whether to uphold or dismiss the impeachment from the day it received the case on Dec. 14.

If the impeachment is upheld, Yoon will be removed from office, triggering a snap presidential election within 60 days. If it is dismissed, Yoon will be reinstated. (Yonhap)