On Sunday, police arrested both the current and former heads of the Defence Intelligence Command in connection to the insurrection allegations, Yonhap reported.
Prosecutors said they were also seeking an arrest warrant for the head of the Army Special Warfare Command Kwak Jong-keun, according to Yonhap.
Kwak is accused of sending special forces troops to parliament during the martial law bid – sparking a dramatic confrontation between soldiers and parliamentary staff.
The head of Yoon’s ruling People Power Party (PPP), who is facing growing calls to resign and who had expressed support for the impeachment, is also due to hold a press conference on Monday at 10.30am local time.
The South Korean government has meanwhile sought to project an air of business as usual.
Acting president Han on Sunday held a call with US President Joe Biden, who underscored the strength of bilateral ties.
Han has also ordered the military to “enhance vigilance” against North Korea, with which the South technically remains at war.
