Special investigation units to probe President Yoon Suk Yeol's sudden declaration of martial law that lasted six hours and threw the country into chaos are being formed as he faces an impeachment vote Saturday at 7 p.m.

The prosecution's investigation team will be led by Park Se-hyun, chief prosecutor of Seoul High Prosecutors' Office, according to officials.

The day before, Prosecutor General Shim Woo-jung ordered prosecutors to open their own investigation and assigned the case to a public security investigation division at the Seoul Central District Prosecutors Office. Shin told reporters outside his office that the investigation will be conducted "in accordance with the law and principles."

Korean National Police Agency's National Office of Investigation in charge of security investigations said in a notice sent to reporters that it has established a martial law investigation unit comprising some 120 personnel. The team will look into four complaints filed to the police as of Thursday accusing Yoon and others of treason, insurrection and abuse of power regarding Yoon's declaration and lifting of martial law Tuesday.

The complaints were filed by the main opposition Democratic Party of Korea, minor opposition Rebuilding Korea Party and Jinbo Party, as well as some 59 chairs from the Korean Confederation of Trade Unions.

Later in the day, the Supreme Prosecutors' Office said it would jointly probe the martial law case with military prosecutors and related personnel as many high-ranking military officers are involved.