South Korean police arrested former Defense Minister Kim Yong-hyun on Sunday for his alleged role in President Yoon Suk Yeol's attempt to impose martial law, according to Yonhap News Agency.
Kim was considered a key figure in Tuesday's short-lived martial law decree. He had already resigned as defense minister.
Police have launched an investigation into Kim, as well as Yoon and martial law commander Park An-su, for alleged insurrection.
Police also raided Kim's home and placed him under a travel ban, Yonhap reported.
Bid to impeach Yoon fails
Yoon, who had declared martial law on Tuesday night and reversed the decision hours later, survived an impeachment vote in parliament late Saturday.
The motion needed the approval of at least two-thirds of the 300-seat South Korean National Assembly to pass.
But it failed after Yoon's ruling People Power Party (PPP) boycotted the vote.
The PPP claimed after the vote that it had blocked the motion to avoid "severe division and chaos."
The ruling party added that it would "resolve this crisis in a more orderly and responsible manner."
Meanwhile, the opposition said it would not give up its attempt to impeach Yoon.