South Korea's leadership crisis deepened on Sunday as prosecutors named President Yoon Suk Yeol as a subject of a criminal investigation over last week's martial law attempt, a media report said, and his former defense minister was arrested.

Yoon survived an impeachment vote in the opposition-led parliament late on Saturday, prompted by his short-lived attempt to impose martial law on Tuesday, but the leader of his own party said the president would effectively be excluded from his duties before eventually stepping down.