"I apologise to the people for having to resign as I cannot continue to perform my duties under severe domestic and international economic conditions," Choi said, according to the Finance Ministry.
His resignation marks the latest twist in South Korea's ongoing leadership crisis. Choi had been set to take over as acting president at midnight following Han's resignation earlier Thursday. Han had announced his stepping down as he prepares to throw his hat into a presidential election set for June 3.
The election has been triggered by the ouster of former President Yoon Suk Yeol, a conservative who was removed from office in April after a failed attempt to impose martial law at the end of last year.
Adding to the uncertainty, the Supreme Court on Thursday found Lee Jae-myung - the front-runner in the presidential race - guilty of violating election law, casting a shadow over his campaign.
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So far, Lee, former leader of the main opposition Democratic Party, has secured his party's nomination and holds a commanding lead in national polls.
