South Korean prosecutors opened an investigation into President Yoon Suk Yeol, his interior minister, and the now-former defense minister for their roles in an attempt to impose martial law, Yonhap news agency reported Thursday.

Kim Yong-hyun, who resigned as South Korean defense minister over his involvement in Tuesday's martial law order, also faces a travel ban as prosecutors investigate, Yonhap said. The other two do not face such bans.

Citing unspecified threats from "anti-state forces" and obstructionist political opponents, Yoon imposed martial law for about six hours before reversing course after parliament voted to oppose the move.

Yoon now faces an impeachment vote on Saturday.